Cad cell relay / protectorelay FAQs for oil burners:

Questions & answers about the reset-button or resetting cad cell relays / protectorelays used on oil burners.

This article series explains the operation, use, and reset button on Cad Cell Relay Controls, including the cad cell works to "see" the oil burner flame, what goes wrong in an oil burner that the cad cell "eye" can detect, and how cad cell sensors are tested using several methods including a VOM.

We include cad cell trouble spots - particular oil burner installations or conditions that can make it hard for the cad cell to sense even a good flame.

Oil Fired Furnace or Boiler Cad Cell Relay / Protect-O-Relay FAQs

Questions & answers about cad cell relay or protect-o-relay primary control reset and reset button problems posted originally at this article RESET SWITCH, CAD CELL RELAY - topic home.

On 2019-08-23 by (mod) - heat primary control lights flash, heat won't run: diganosis

Allen

Some common problems to check before replacing the control:

1. a dirty cad cell sensor eye

2. bad cad cell sensor eye - easy, it's a trivial plug-in replacement

3. bad cad cell wiring connection

4. oil burner improperly adjusted, producing too much soot

5. causes of the item above, such as an air leak in oil piping or at the oil filter

The cad cell can be simply wiped off but most techs prefer to kill off possibilities 1 & 2 by just plugging in a new cad cell sensor.

Look on your primary control or cad sell sensor (usually a black or gray box atop the oil bureer) and confirm that the yellow (usually) wires from the cad cell sensor eye are connected thereto.

Now attach a photo of the control and its labeling - we need to know the brand and model to make sense of the cad cell sensor warning LEDS or blink codes.

On 2019-08-23 by Allen

About 3 weeks ago my oil fired water boiler shut down. It's a Weil-McLain, WTGO-4 I think. I changed the basket filter, the pump strainer, and the nozzle and it ran OK for about a week. Now when it shuts down I reset it and it runs for 3 days or so, sometimes more, sometimes less.

It usually starts back up no problem but the other day I read the label on the, I think it's the relay, and it tells how the light can flash for either 1/2 second or 2 second intervals.

When I reset it, it was flashing 1/2 second intervals, it ignited and ran for about 15 seconds and then shut off and the light was now flashing 2 second intervals. About 15 seconds later it came back on without resetting it and fired up and ran fine, again for about 2-3 days. Does this sound like a bad or dirty cad cell? If so what do I use to clean the cad cell?

On 2019-02-19 by (mod) -

Steve I agree that it's possible that the control was damaged by a power surge.

Take a look at the control test procedures for the R8184 given in the manuals {PDF files] above on this page.

On 2019-02-19 by steve

After a power surge at my home, my relay switch reset's but furnace will not start. It is a honywell r8184g4009 relay.

On 2019-01-27 by (mod) -

John,

Thanks for asking about thermostat wire connections when we have both an aquastat and a separate Cad Cell Protecto-Relay both of which have terminals marked T T for Thermostat wires. I should have made that clear.

You'll see terminals marked T and T or T1 and T2 on most controls intending to accept thermostat wires. Just as you thought.

But when the Thermostat is wired to the aquastat, typically the TT terminals on the cad cell are jumpered together. YOu'll see that in this old cad cell relay photo that appears in the article above and that I'll post again below.

My ruler is pointing to the yellow wires that run to the cad cell eye. To the right of those is the T-T jumper wire.
IMAGE LOST by older version of Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2019-01-26 by JOHN STREP

were do you wire the thermastat to the aqua stat relay or the protector relay? I had a Honeywell R4184D1027, Oil Burner Primary
Control 45 second , i replaced with R818G . it has the T T connection, but my thermostat is connected to my HONEYWELL AQUSTAT L8124A do i jump the T T wire,s and if so, will that then activate the relay and hold it on all day long

On 2019-01-10 by (mod) -

It is possible that the arc damaged a control board in the primary control - yes. Or possibly a voltage surge damaged the cad cell eye itself - an inexpensive part to replace, which is why many techs just try swapping in a new eye right-off, even without testing resistance (as I recap again below).

( I don't think there are any Cad Cell relays / primary controllers that use an independent internal fuse that would have blown. )

Here are some additional Cad Cell diagnostic tips from Beckett

To understand how to troubleshoot the cad cell, it is important to first know how the control operates. Initially, the control must have a high resistance across its F-F terminals (cad cell does not sense visible light) before it will attempt to start the burner. If the cad cell senses light or is shorted, the relay in the primary control will not pull in to start the burner.

Once the burner is running and the flame is established, the cad cell must have a low resistance (cad cell sensing flame) to keep the primary control from locking out on safety.

First:

What if the burner will not start and the cad cell is suspected? The procedure for solving this problem would be first to make sure the thermostat is calling for heat and that there is line voltage to the control. Then remove one lead of the cad cell from the F-F terminals. If the burner starts, this suggests that the cad cell is either seeing external light inside the housing, cad cell wires are pinched, the assembly is shorted, or the cell is defective. You may need to shield the cell from external light, repair pinched wires, or put in a new cad cell.

OR
Second:

What if the burner starts but locks out and the cad cell is suspected? This symptom initially shows that the control did see the high resistance necessary to start the burner. However, during the lock-out timing period, it did not sense the low resistance on the cad cell necessary to keep the burner running.

As stated earlier, the control must have no more than 1600 ohms of resistance to prevent random lock-out.

Beckett gives these

3 Cad Cell VOM test Ohmeter readings

• Less than 1600 ohms but not zero. Cad cell operating properly.
  
• Above 1600 ohms but not infinite. Defective or dirty cad cell, misaligned sighting of flame, or improper flame adjustment. Clean cad cell and check for proper sighting of flame. Check for proper flame adjustment. If cell is defective then replace.
• Infinite resistance. Open circuit. Check for broken cell, holder, or wire. Loose cad cell in holder. If defective, replace necessary parts.

- retrieve 2019/01/09 original source and more from Beckett: www.beckettcorp.com/support/tech-bulletins/troubleshooting-the-cad-cell/

On 2019-01-09 22:59:39.564154 by Randy McIntosh

I did not turn off power when I changed switch and I touched side of outlet box causing an arc, now oil burner motor will not come on , could I have damaged primary control or what else could have been damaged to cause motor to not run, when I turn on power green light on primary control blinks one time and only blower motor comes on

On 2019-01-09 21:08:59.559415 by (mod) -

Randy

because you are describing what sounds like an electrical short, for safety you need to turn power off to the oil burner circuit entirely and call for an electrician to inspect and repair the shorted or damaged wiring or switch.

On 2019-01-09 21:01:21.071950 by Randy McIntosh

Oil burner motor was working but I had an arc at furnace switch now only blower motor comes on

On 2019-01-08 00:10:54.531455 by (mod) -

It's normal for the cad cell relay to need to cool down before you can reset it. Certainly a minute or two would be normal.

When the cat's tail is tripping intermittently I look first for a system that needs cleaning and adjustment. You could also have something as simple as a loose or corroded electrical connector or there could be something a little more subtle such as a failing Transformer or ignitor.

And of course don't forget to assure that you have good fuel flow and not a dirty, clogged oil filter.

On 2019-01-07 23:56:43.866032 by Bib Distefano

My relay keeps tripping, some times after hours, some times after minutes. It needs to sit a while in order to reset, any help appreciated

On 2019-01-08 by (mod) - My relay keeps tripping

It's normal for the cad cell relay to need to cool down before you can reset it. Certainly a minute or two would be normal.

When the cat's tail is tripping intermittently I look first for a system that needs cleaning and adjustment.

You could also have something as simple as a loose or corroded electrical connector or there could be something a little more subtle such as a failing Transformer or ignitor.

And of course don't forget to assure that you have good fuel flow and not a dirty, clogged oil filter.

On 2019-01-07 by Bib Distefano

My relay keeps tripping, some times after hours, some times after minutes. It needs to sit a while in order to reset, any help appreciated

On 2018-09-23 by (mod) - try replacing the cad cell sensor

Dez,

A new cad cell is not costly; have you tried replacing it (even though your test found the old one appearing OK?)

Have you tested the wiring harness continuity ? If indeed the cad cell is clean and properly aimed (confirm by testing its signal when flame is present) then a bad plug or wire or connector can cause the trouble you describe.

On 2018-09-23 by Dez

@Smitty, I'm in the same boat. I am a competent do it yourselfer'. Have working knowledge and a hard study of the system.

My only limits are the specialized test equipment, oil pressure gauge, CO2 and 02 tester etc.. My furnace lights off fine, good looking flame, no blow back or smoke, exhaust and chimney clean and inspected, intake is clean. I have a Beckett oil pump on a forced air Furnace,....

electric motor is good, squirrel cage blower-good, electrical contacts -all good, oil tank is full, lines bleed repeatedly, oil pressure flow appears adequate when bleeding -all good, nozzle changed, then old one reused to double check fault,

CAD cell cleaned (wasn't hardly dirty) tested good with ohm meter and is aimed at flame, with multiple aiming adjustments attempted, bracket and wires look good (wires not pinched, contacts at transformer clean and tightly secured with screws, all-good.

Gun and electrodes inspected, nozzle-to-electrodes-distances set to spec and tested for spark -all good, transformer operates electrodes fine, lights off oil, but still trips reset anywhere between 15-45 seconds.

Flame is looking great as I watched the reset button trip. Reset button was tested, turns off pump when pressed while furnace is running.

I can't freakin find the problem! I live in Maine and it's Fall, morning temps are now dropping down into the 30's. You can also reach me at dezdon@roadrunner.com with ideas if this board goes silent.

On 2018-04-17 01:08:37.246981 by Anonymous

Do not keep restarting your furnace. That invites a puffback explosion. You need to call for service

On 2018-04-16 22:38:11.391106 by Dale Jennette

My oil furnace will not start unless the red button is pushed . It started from time to time .

Now it has to be pushed . It now has to be pushed numerous times and when it shuts off it will not come back on unless the button is pushed again .

It doesn't even try to start . Could it be the relay and how can I test it ? Thanks

On 2018-03-16 by (mod) - service man changed the cad cell eye - dissatisfied customer

Eileen

I don't want to offend the service techs by pretending I can see more from here in Mexico than they can see at your home when diagnosing an oil burner or control problem.

But I can suggest this:

If the cad cell is being replaced repeatedly it may be that it's because it was either sooty or damaged by excessive blow-back heat in the combustion chamber. Either of those conditions would kill the cad cell, But replacing it does not fix the underlying problem: improper burner adjustment.

The fact that you see burning around the burner-mount area is an indication of too-hot and improper operation, perhaps a draft or combustion air problem.

The cad cell eye itself is a small sensor that is not expensive, less than $15. USD, and it simply plugs-in to a socket on the end of a wire that connects to the cad cell relay control. So replacing it during service is a trivial step.

Many service techs try to repair a problem by replacing a lower-cost, easy-to-replace part, as that can be less costly to the customer than a protracted diagnostic visit.

That's especially true if a problem seems to be intermittent and thus hard to track down.

Use the picture frame icon to the right of the Comment button to show us photos (one per comment) of the entire Bradford White heater (I suspect this is a water heater), and closer images of the oil burner and of the burned area, and I may be able to comment further.

I'd also want to see the flue vent connector and entry into the chimney made by the water heater as well as an outdoor view of the chimney top.

On 2018-03-14 by Eileen

I have a Bradford White furnace, not too old. I had a control unit that I believe was replace once already. My hot water went off.

Called a repair man. He came and change the cads eye. Hot water worked for a week or two. Went off again. He came replace the Cads cell eye again. It went off again in a week or two.

I don't use much hot water as I live alone. I called a different company. He came spent a good time in the basement. He replaced the control unit. Cost me $500. 2 months later or so it went off again.

I called, told the answering service that it should be under warranty. Someone came and replaced the Cad cell eye. I got an additional bill for $250. This is my question as I am challenging the bill.

I said that the cads eye cell is part of the control unit system and why would the repairman give me a new unit right off the bat, when I told him that the previous repair man thought the cads eye was the problem.

I said I wonder why he would not change the whole cads eye unit relay first, test it with my old control unit first before selling me a new control unit. He said firstly that the cad eye cell in not part of the control unit system. And that this new problem (which he supposed fixed with a new cads eye...

which he now claims he actually changed the cads eye unit ... which I don't believe actually) is a "new problem" although it was the problem I called him to fix in the first place telling him of the previous few visits by the previous company and their attention on the little square piece.

He says it is a new problem because the cads eye/control unit couldn't have worked for 2 months.

I responded that it could have kept working, if it was the wires in the relay or the whole unit that was the problem or something like that...

and besides I don't use much hot water as I am alone in the house. I would love someones opinion on this $750 spending spree. The other thing is that when I first got the Bradford/White heater..

.the area around the circular plate where the fire box is was burning the sheet metal. Turns out that the heater was missing some interior fire box, so somewhere along the line (a few years ago) some repair person stuffed some flame retardant material up into the fire box space. Could that be it..though it was working for years in that state.

On 2018-01-06 19:06:04.080087 by (mod) -

Mike

With a furnace a nice diagnostic is to watch the fan limit switch on a call for heat;

You'll see

- burner comes on

- plenum begins to heat

- the fan limit switch dial begins to rotate

- when the dial index gets to FAN ON the blower turns on

- if the dial continues to rotate and the plenum heats excessively you'll see the dial rotate to FAN OFF at the FAN LIMIT setting

On 2018-01-06 17:43:11.286106 by Mike

Will do. Thanks Dan. That is exactly where I was leaning myself originally but have had others keep pointing me towards the burner, sensor etc. I did pull the air filter last night just to see if that would make any difference but it did not.

Think I will go pull the sides off and get a better look at the blower itself. This is a tenement unit and last occupant had LOTS of dog hair. I had to vacuum a boat load of it out of the return vents. Wondering if it may have made it's way into the blower blades as well? Will let you know what I find. Thanks again!

On 2018-01-06 17:35:17.277955 by (mod) -

Mike

That sounds as if the plenum is overheating, shutting down on high temperature

Look for a dirty air filter, dirty blower fan, blocked or reduced air flow through the system

On 2018-01-06 17:11:20.680874 by Mike

If CAD Cell is the issue, the only way to re-fire the burner would be to press CAD Cell relay, correct? I have a forced hot air unit that just does not seem to be heating properly. Stat is set to 68 but can't get room temp above 60. Blower runs constant and oil burner burns for approx. 3 1/2 min every 7 1/2 min with no user intervention. Plenum seems to be getting plenty warm as I am unable to hold my hand on it, even 3 or 4 min after burner shuts down. Thoughts?

On 2017-12-31 22:56:45.656074 by (mod) -

Smitty,

Did you try the cad cell tests in the article above in the section titled:

Resistance Testing the Cad Cell Sensor using a VOM or Digital VOM ?

Check
- your connections
- the placement of the cad cell - be sure it is seeing the flame
- the face of the cad cell for sooting. Keep in mind that checking oil burner flames by eye is only "ballpark" correct. A flame can look pretty good but be smoky enough to foul the cell or have trouble starting

Check what happens during startup and shut down. Watch the flame and burner to see if you can spot a clue for why it's shutting down. That 30 second on cycle sound to me as if it is shutting down every time as if it is never seeing a good flame.

On 2017-12-31 21:21:51.706228 by Smitty

Carlin burner assembly, was running fine for 2 mos, now have nice clean flame, inspected and cleaned ignitor, gaps good, nozzle clean working great. Replaced CAD eye, reset working, will not run for more than 30 secs ea cycle. Fan thermostat works manually, new motor 2 yrs ago. What now? New Years Eve, prof service not an option, can do myself but stuck. Any other way to check relay or safety shut off? what else may cause this problem?

On 2017-12-30 00:47:03.554862 by (mod) -

If the entire furnace is short cycling I suspected maybe overheating - and that's an unsafe condition that requires prompt repair.

However it's also possible that a loose electrical connection such as a loose thermostat wire could be jiggling around and turning the heat on and off at odd times or frequent intervals.

On 2017-12-29 05:49:04.946497 by Pat

Do you think their is something wrong with my thetmostat, if the heat goes off and on...I wrote a comment befor this one

On 2017-12-29 05:46:34.615979 by Anonymous

Heat is set on 62, any higher the bedrooms r very hot...furnace is always off and on..it's cold outsuse I know but hearing the heat going on and off all the time, I feel their is something wrong....hel

On 2017-10-02 05:03:03.149901 by Rodney Pilch

My r8184g4009 started making a horribly loud rattling noise on my oil fired boiler. I replaced it with a new one. Within 12 hours, it is now making the same obnoxiously loud noise when the boiler goes cold and restarts.

Doesn't do it when the boiler is warm and restarts. Don't know what to look for. A puzzled home owner.

On 2017-09-30 23:33:53.127881 by (mod) -

although there are methods including freezing lines in order to cut and install fittings without having to drain a system most likely for what you describe the boiler system will need to be drained

On 2017-09-30 23:20:44.844452 by al

replacing a backflow preventer in a boiler system with no isolation valves

On 2017-07-05 20:57:20.209077 by (mod) -

Mane

The Honeywell R8184G4009 "Protectorelay® Oil Burner Control with 45 second safety timing, alarm outputs, and manual safety switch" is widely-used as a cad cell based safety control replacement.

To replace an R4184D protectorelay (now considered obsolete) Honeywell has offered

the R8184G4025/U

the R7184U1020/U (universal replacement controls designated by the "U"

and currently recommends a newer control, their

R7284U1004/U Universal electronic oil primary with programmable parameters and LCD display

Any of those would work with your oil burner.

On 2017-07-05 20:28:45.260907 by Mane

Will the oil burner control R8184G4009 work with my old R4184D1027?

On 2017-07-05 by (mod) re: which protectorelays replace the Honeywell R8184G control?

Mane

The Honeywell R8184G4009 "Protectorelay® Oil Burner Control with 45 second safety timing, alarm outputs, and manual safety switch" is widely-used as a cad cell based safety control replacement.

To replace an R4184D protectorelay (now considered obsolete) Honeywell has offered

1. The R8184G4025/U
2. the R7184U1020/U (universal replacement controls designated by the "U"
3. and currently recommends a newer control, their R7284U1004/U Universal electronic oil primary with programmable parameters and LCD display

Any of those controls would work with your oil burner - I'd prefer Honeywell's latest recommendation, their R7284U1004/U the Universal electronic oil primary with programmable parameters and an LCD display, shown just above. Honeywell's product literature describes this product and includes these features (this is a partial list):

• Enunciation of status and faults via LED or display
• Models with LEDs monitor igniter and cad cell
• Models with display monitor igniter and cad cell, and alerts technician as to exact cause of lockout
• Error history and baseline readings provide system performance and trends on models with display
• Non volatile memory for settings and diagnostics
• Extensive, actionable diagnostics (display models only)
• History detailing last 10 events (display models only)
• Continuous state and CAD cell readings (display models only)
• More details from Honeywell are at https://customer.honeywell.com/en-US/Pages/Product.aspx?cat=HonECC%20Catalog&pid=R7284U1004/U

On 2017-07-05 by Mane

Will the oil burner control R8184G4009 work with my old R4184D1027?

On 2017-05-28 by (mod) re: can a bad cad cell cause flooding of the oil burner combustion chamber?

Bill:

A cad cell failure itself - that is the cad cell that senses the presence of the oil burner flame - would, by failing to send a "flame present" signal to the primary control or protectorelay, most-likely leave the burner OFF rather than causing flooding of the combustion chamber with oil.

So while I cannot possibly know from just a brief e-text, I suspect the problem is elsewhere, in the primary control or in a human error.

What sort of human error? Well if someone keeps pressing the reset-button on the primary control that can cause repeated efforts to run the oil burner without successful ignition. Each of those startup attempts will pump some oil into the combustion chamber.

On 2017-05-28 22:18:06.872994 by Bill

Can a cad cell be defective and not shut an oil burner off and flood the chamber

On 2017-04-29 by (mod) re: oil burner doesn't shut off and there is no flame

Jim

Watch out: I would leave that oil burner OFF and call for repair.

What you describe is very dangerous: leaving un-burned fuel in the oil burner combustion chamber is asking for an OIL BURNER PUFFBACK EXPLOSION (use the search box just above to find that article to see details)

On 2017-04-27 by JIM

i noticed that my burner dosen't shut down when there is no flame.

On 2017-03-18 by (mod) re: signs of a bad oil burner transformer

Daniel

Indeed a bad transformer means weak spark means oil burner start-up and run problems that can leave the system off on reset.

Don't worry, yet, about the cad cell button not popping all the way back up: give the system say 5 or 10 minutes in the OFF state. The relay needs to cool down before it will let you reset-it.

Then if the system keeps going off on reset more repair is needed: perhaps a burner cleaning and nozzle replacement. Search InspectApedia.com (search box above) for OIL BURNER WON'T RUN to see other diagnostics. But try what I suggested first.

On 2017-03-18 by Daniel

Hi, my oil company came and told me the transformer was the problem fixed it and it ran once. now the button my cad cell relay wont pop all the way up when it runs and it shuts off after 15 seconds. he said to replace that for 300..i went to home depot fixed it for 110 but the same problem occurs. What could be wrong?

On 2017-02-23 by (mod) re: furnace keeps popping up the reset button - is it a bad control?

Right Brian. The reset switch relay has to cool off for a time before it will allow you to reset the sytsem. DO NOT keep pressing the button; if the system dosn't keep running and you keep resetting your risk a PUFFBACK EXPLOSION - search Inspectapedia for OIL BURNER SOOT & PUFFBACKS to read more.

Time to call for repair: the control may be ok - there are a number of problems that cause the system to go off on reset - even just a dirty oil burner nozzle.

On 2017-02-23 11:11:03.219063 by Brian Britt

furnace will run for several cycles and then the reset button pops up and will not reset for awhile. Is it the honeywell control going bad or the cad cell?

On 2017-01-06 22:44:44.164372 by (mod)

Thanks for the suggestions for Jim, James B. It's a very nice, condensed diagnostic sequence.

I'd have added that a homeowner needs to be careful when fooling with these parts since making a mistake can lead to more trouble. Simply over-tightening a nozzle can strip threads on the nozzle adapter or burner oil line and lead to an ugly oil spray mess that is in turn unsafe.

We much appreciate technical content suggestions, contributions, critique, and are happy to cite and link-to such contributors (send that info by email found at our CONTACT link) - Working together makes us smarter.

Daniel

On 2017-01-06 by James B. -HVAC Tech. - how to fix oil burner short cycling

Jim- You'll need to do a few things to get the furnace firing correctly again.

1st: replace your fuel nozzle & oil filter (inspect the oil filter, is there sludge in the canister?)

2nd: prime your fuel pump (bleed the pump of contaminates/air until a steady flow of fuel appears) .

It'll take the furnace 2-5 cycles to successful feed the fuel through your system until continuous combustion occurs.

If still no flame then 3rd: replace fuel strainer/gasket, listen to the fuel pump (is it working but real loud, it's stressing to do its job which is an indication of a plugged fuel line) .

If still no flame check for water in fuel tank, wrong air mixture, electrode settings or the control voltage. If still no flame after all that call an HVAC technician. Hope this helps.

On 2017-01-01 by (mod)

JH,

Could be a loose wire, bad cad cell, or poor thermal contact between the aquastat sensor and the well into which its inserted. Or, of course, something else.

On 2017-01-01 by jh

Smith boiler is short cycleing runs sometimes 10 seconds then off.Flew is real clean.Then sometimes its fine.Could it have anything to do with the problem

On 2016-12-12 by Jim

Daughters oil tank was siphoned empty, she had oil delivered and fired up the furnace before I got there and the burner fired right up and ran and then shut off.
Not knowing she hit the reset switch and it fired again and ran for a while and shut off again and she kept doing it until it would not fire at all.

When I got there the light on the reset was flashing and the indicator light was on staying on for 1/2 second and the display said that burner was in lockout.
Any suggestions?

On 2016-09-19 by (mod)

Humming is often at a relay that's on the road to the Timbuktu of Failure.

On 2016-09-19 by Ralph D.

low hum in the primary control when the power to the furnace is on and is set to the no run position on the thermostat.

Reader comments: ohmeter readings on cad cell relays & sensors

[delete] (Feb 11, 2012) Tony said:

Hi, I love the work you guys do and think it can be a life saver when you may have exhausted all options.

My comment is with regards to the section entitled "How to Test the Oil Burner Cadmium Cell Relay Switch", the sub titled, "Testing the Cad Cell Sensor Itself" section found in RESET SWITCH, CAD CELL RELAY.

You mention that an ohm reading on the flame sensor terminals when the boiler is running should be .5 to .6 I took an ohm reading after having cleaned soot from an obstructed cad cell and got an ohm reading of 500 to 600.

I though my flame sensor was faulty. But then i opened the canopy containing the flame sensor and shined a 100 watt light (137 foot candles of illumination) bulb at the flame sensor with my friend taking the readings and compared the results to a specs chart on the flame sensor that charted foot candle power vs ohms and saw that 500 to 600 ohms was correct.

I realize i took the reading while the boiler was off but the wires from the cad cell to the terminal screws where connected and that may have given me a skewed reading but i just wanted to point out the difference between your recommended ohm results and what is observable to an average joe like me. Thanks

...

Continue reading at RESET SWITCH, CAD CELL RELAY or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see

BOILER CONTROLS & SWITCHES

RESET SWITCH, HEATER REPAIR - how to fix a cad cell relay that has lost its red reset button

RESET SWITCH, ELECTRIC MOTOR

STACK RELAY SWITCH

FURNACE CONTROLS & SWITCHES

WATER HEATERS OIL FIRED

Suggested citation for this web page

CAD CELL PROTECT O RELAY FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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