Cad cell relay / protectorelay diagnosis and repair FAQs for oil burners on boilers, furnaces & water heaters.

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 RESET SWITCH, CAD CELL RELAY - topic home. Be sure to review the troubleshooting advice given there.

Watch out: Don't press the primary control reset button repeatedly. If you keep trying to restart an oil burner without it running successfullly, excessive un-burned oil in the combustion chamber can cause as puffback explosion when ignited.

Weil McLain boiler keeps going off on reset and puffs smoke when I push the cad cell relay reset button

I have Weil Mclain boiler & in the last 4 days needed to be rest daily. After reset it starts right up & runs perfectly. All I noticed was a little puff of smoke just after pushing the rest button. The heating tech came today & said everything looked OK except replaced the cad cell.

However, I needed to rest again tonight. I asked them to come back tomorrow. Do you have specific things I should ask
thanks On 2018-01-03 by Al

by mod -

Al,

Replacing the cad cell sensor is a standard thing to try .

There are other things to check.

Beyond that we look for a air leak in oil piping or a subtle and sometimes hard to spot damaged oil burner electrode insulator, or, intetmittent transformer failure.

Should I replace my oil burner and control relay if the burner stops working?

Worked for ~ 18 hrs then shut off again. Not sure if should suggest replace burner motor & contacts. Does anyone have any diagnostic ideas or suggestions.
Thanks, Al On 2018-01-05 by Al

by (mod) -

I would not rush to replace a burner motor, as that's a rather expensive shotgun approach.

First we need to diagnose the problem. Your oil burner may need simple cleaning and adjustment, a new nozzle, or other inexpensive part.

I agree that intermittent failures are difficult to track down.

I'd expect a service tech to make some other inspections and tests of
- the high voltage transformer

- the condition of the electrodes & their insulators

- the oil line (vacuum test) for air leaks

- a bad relay in the primary control

When the burner shuts off, if the reset button has popped that's diagnostic of a fuel or flame problem or a cad cell sensor or cad cell relay primary control problem.

by Al Tech replaced the Primary control on the oil burner with a Carlin 4223002S but an ignition problem remains

Tech came & replaced primary control unit with Carlin 4223002S.

After ~ 1/2 hr the unit showed red light meaning lockout. Hit reset button once & it started right up.

Does this mean a problem with sometimes not lighting properly. Heating guy is coming back. Any further suggestion?

thanks again,

Al

by (mod) -

it sounds as if we haven't yet found the reason the burner is not starting or not running properly, and the safety control is doing what it should.

by Al - fixing wiring and replacing the oil burner nozzle solved the problem

Different heating guy ( more senior) from same company came back.

Needed to adjust some of the wiring of the new control unit.

Also he said the nozzle needed replacement.

Hopefully the problem will now be fixed..Will let you know over the next week if everything is still working.
Thanks, Al

by (mod) -

Very encouraging. Let me know what wiring changes were made if you can. Keep us posted

 

I have to tap the cad cell relay box to get the burner to kick on

Every morning I have to go downstairs and tap the Cad Cell Relay Control box to get the burner to kick on. Same thing when I get home from work- not much of a tap either.

The thermostat is the Honeywell RTH2300 / RTH221 series and its set to be 63 at night and when I'm not home, and 70 from 5pm-11pm. I've been waking up to 55 degrees.

We just had the control box replaced last week and nothing has changed.

What could be the issue? (Mar 15, 2016) Sheehan

Reply:

Tapping to get any electrical component working sounds to me as if there is a loose wire or failing connection or relay inside the control.

If replacing the control box did not address the problem then the failure is probably not inside the control box itself but perhaps in a connection to it or a connection nearby - even the plug-in socket of the cad cell sensor itself.

Details about cad cell relay inspection and troubleshooting are at RESET SWITCH, CAD CELL RELAY 

You might call your oil company service manager and ask for help from an experienced, senior service technician. Keep us posted. What you find will help others.

I don't think the problem is the Honeywell themostat that you cited, but here is a copy of the Honeywell RTH2300/RTH221 Series Programmable Thermostat Owners Manual [PDF]

I have suffered from Cadmium poisoning: could my heating boiler cad cell be the cause?

I received and respect your response to my recent email. I do not expect a response to this email, but wanted to ask a question because I have exhausted every resource I can think of. In June 2010, I learned that I had long-term carbon monoxide exposure.

After months of treatment, I am very improved. I do biochemical testing and I ordered several tests on myself as no one had done any lab testing or even thought it could be relevant to the downstream effects of CO poisoning.

I have very high levels of cadmium in my blood, indicating a "recent" (un definable term) exposure. I wonder if the cadmium could have come from the cad cell relay on the gas hot water heater.

To my knowledge, I was not in contact with any of the common sources of cadmium. I will be testing my home and my family members' blood. Over the past six months, I have put together a team of over 20 people to help treat the effects of the poisoning.

I am doing well and believe that some of the data I have collected might be of interest to you. Please let me know if that is the case. I know you are very busy--and I love your site. - A.S. Louisville KY

Reply: Cad Cell is Unlikely to Be a Hazard, Here's What & How to Check

The cad cell that is used as a flame sensor in heating equipment is quite well sealed-up. In my OPINION there is no reasonable chance that a heating boiler cad cell relay cad cell sensor would explain cadmium poisoning in a person's home.

After all cad cells are used in a combustion chamber and exposed to challenging conditions such as high temperature and vibration.

We do not know how much cadmium is used in that flame-sensing device - the manufacturer could tell you.

But if nevertheless you suspect that the heating boiler or water heater oil burner cad cell sensor itself is a source of cadmium, it would make sense to have the cad cell removed with care, placed in a sterile clean container, and tested for leakage.

I'm somewhat doubtful that you'd find something. My reasoning is that if the cad cell were damaged most likely it also would not be working and you'd have noticed - you'd have no heat because the oil burner would stop running.

Cadmium is used in other products, including some paints. If you've been hanging around an artist's studio ask about her paints. Some other common sources of cadmium include those listed below, all of which seem to us to be potentially greater total cadmium reservoirs than a single sensor in a heating appliance:

• Auto exhaust can move cadmium into soils around highways (and into the air)
• Some batteries or battery manufacturing facilities
• Metal containers (some such as some ice cube trays or even bowls)
• Foods: certain grains, potatoes, vegetables, depending on the soil in which they are grown - so watch for spinach grown along a busy highway; some shellfish are high in cadmium.
• Metal water piping if the water supply is chemically aggressive and leaches out cadmium
• Natural occurrences at very low levels in the soil, in air, and even in water.
• Nearby industrial waste burning plants, metal plating or metal working businesses
• Tobacco smoke, smoking or being around smokers, possibly also from cigarette papers
• Paints (some, not all) particularly in some paint pigments ("cadmium yellow")
• The U.S. EPA has some helpful and rather authoritative articles on cadmium sources, cadmium poisoning, and particularly worrisome cadmium sources. For example see the U.S EPA website on Lead and Cadmium in toy jewelry - http://www.epa.gov/lead/pubs/toyjewelry.htm

As you are consulting a panel of experts, it makes sense to ask them to look at your personal case history and to compare that with the environments in which you've spent time, checking to see if you've been exposed to a particularly likely source of cadmium.

 

What are the proper ohms readings at a cad cell relay

At times I can't get an under 2000, or even 3000 ohm reading after ruling out or correcting the following:

- poor atomization

- dirty burner fan

- electrodes

- continuity

- cad cell eye

- re-positioning cad cell etc...

- Samuel Zapata

Reply:

Samuel,

Sometimes as continuity check can miss a bad connection, but in any case given what you describe, it would be an inexpensive and trivial step to just plug in a new cad cell sensor and repeat the tests.

The reset of the components are very straight forward, as you've described.

You can test the cad cell's response to light before placing it back on the burner assembly.

That step will tell you if the problem is the cad cell and its wiring or a smoky dirty burner operation.

How do I set my VOM to test a cad cell

What ohm setting should I set my digital or analog vom to test a cad cell? On 2018-01-22 by Joe

by (mod) -

In Ohms mode set your meter to its lowest or most-sensitive range.

 

My oil fired furnace fires up but the blower in the air handler doesn't turn on - is it the cad cell relay?

I have a oil-furnace,my system fire up,blower didn't come on system shut down .I replaced the limit control, system fired up,blower came on ran a few sec. then shut down.

I suspect cleaning or replacing the flame detector. I see soot on cabinet,am I close? - Victa

Reply: soot in the oil burner combustion chamber can foul the cad cell sensor "eye"

Victa, that's a reasonable first guess.

Have the oil burner cleaned and serviced and include replacing the cad cell sensor.

 

What do do if my oil burner keeps tripping at the cad cell relay

My oil burner keeps tripping at the cad cell relay I replaced the cad cell sensor and it's still doing it the burner will run for 10 to 12 hours fine and then trip off should I replace the whole relay - Bill

My oil furnace comes on sometimes I have to hit the reset button on the relay, then it goes on then off periodically while heating the house. What is likely the problem? - Ed

Reply:

Bill and Ed: if the oil burner keeps tripping the cad cell relay and the relay sensor has been replaced, more likely the burner is running at too high a smoke level - running dirty- and needs cleaning and adjustment. The root cause could be several things: inadequate combustion air, bad nozzle, improper electrode adjustment etc.

 

My furnace is not firing even though the thermostat is calling for heat - cleaning the cad cell eye didn't help

My furnace is not firing even though the thermostat is calling for heat. It is only when I hit the relay reset will the burner fire. The furnace then will run until its satisfied then turn off like normal. It runs correctly one or two more times when the thermostat is calling but then the same issue will occur.

I tried to clean the eye on the sensor but it didn't make any difference. I also jumped out the thermostat (without hitting the reset) and the furnace did not fire. Should I just buy a new cad eye sensor or does this sound like a different issue all together? - Adam Kelly

Reply:

Adam,

Presuming your thermostat is calling for heat properly, it's certainly a trivial plug-in repair to try a new cad cell eye. But if the cad cell were bad I'd think that the burner would not continue to fire after startup. Try it anyway and let us know.

As you may already realize, when a burner is going off on reset that normally indicates a problem with the flame sensor (your theory) or with the burner flame itself.

IF that doesn't work you'll need to check some other possible causes:

- loose or bad electrical connection at the sensor or controls

- dirty nozzle, electrodes, burner turbulator

- bad transformer

 

The red reset button on the Protectorelay cad cell control keeps popping

The reset button on the oil primary keeps popping daily. I have had the oil furnce tech in to clean the furnace and replace the nozzle, filter, etc. I have replaced the fan motor last year and recently replaced the photo cell. I have heard the fan motor turn on however no light-off since the cleaning. What could be my possible problems and fixes? Tranformer?? Weak primary?? Thanks, Trent - Trent 1/6/12

Reply:

Trent,

If the oil heat service tech watches the burner start cycle s/he may at least be able to observe whether or not there is a difficulty with the flame start-up or not. A range of problems including a weak transformer, even a bad electrical connection, a defective fuel unit, dirty oil filter, etc. can cause intermittent startup difficulties.

There are oil heat equipment tests that can check out the transformer output, the oil line vacuum into the fuel unit, output pressure from the fuel unit, cad cell relay sensor (have you tried replacing the sensor element), etc.

 

We keep losing heat and the cad cell and protectorelay trips off

My oil furnace occasionally does not light. It has been cleaned, inspected and gapped and the transformer was changed. It fired w/o problem for approximately one week then began to trip the cad. When reset, the transformer can be heard working when it lights (a faint buzz) yet when it does not light there is not a sound from the transformer.

Both the old and new transformers were bench tested and function fine. Since the blower and transformer are wired to the same leads and the blower always works what should I have the technician check next? - Brian C 2/12/12

Reply:

Brian

A repeated tripping cad cell usually means the system is running dirty or losing flame; it's easy to check and rule out a bad cad cell sensor itself as part of the troubleshooting - described in the article

RESET SWITCH, CAD CELL RELAY .

 

Oil fired water heater won't start - I pressed the reset, nothing happens

my hot water oil-fired burner does not come on just put 50 gallons of fuel in, the boiler must have been down at least 1 to 2 months,what should i do,

i have call for heat but no flashing lights on the transformer for my diagnostics so i cant reset the system nothing happens this is the first time this happend ran out of fuel before but always had no prolem starting back up, what should i do,it cant be the cad cell because i cant start the motor i need some help asap thank you!!!!! - Harvey 3/12/12

Reply: check electrical power

Harvey,

I'm not sure your oil delivery of just 50 gallons was sufficient to guarantee an oil flow to the oil burner - it depends on tank size and what was in the tank.

If really NOTHING happens, then your system has lost electrical power.

If the burner motor turns on but the burner won't ignite, quite possibly if the burner won't start and run it's because someone needs to bleed air from the fuel line; also when a system has been shut down for a long time it makes sense to change the filter, fuel unit screen, and to inspect, clean, and if appropriate change the oil burner nozzle, then check air settings and flame smoke level.

 

Thermostat calls for heat but nothing happens, how do I test the safety switch?

Eventhough I have the thermostat calling for heat my furnace still hasn't fired up. Is it possible that the (R8184G) not sending the signal or needs replacing? Is there anyway of testing this switch? - Russ 11/11/12

Reply:

Yes as in the article RESET SWITCH, CAD CELL RELAY

 

Flame sensor cad cell eye keeps tripping the primary control off: service tech says cleanout is needed

So last winter we had a power outage, all was well until then. After, the flame sensor would trip once and a while, then got progressively worse. I've replaced the sensor, and the controller, but the issue remains. If I short the sensor (after ignition) the system runs.

I've cleaned the sensor, thinking it was fouling, but if I move the sensor to a viewing port (holding it in place) it appears to work fine. The port where the light comes in appears to be clear. We did have a service person come out shortly after the initial issue, but he said "I don't know, I can do an annual service, maybe it will help" - nope. Short of replacing the furnace, I'm stuck. - Gunter 12/14/12

Reply: your sevice tech is right

Gunter,

Some other reasons that a good cad cell and control keep tripping off the oil burner include

- the cell mount position is not quite correct, or a mounting bracket has been bent, so that the sensor eye doesn't properly see the flame;

- the oil burner is out of adjustment, running dirty, making a smoky flame - your service tech could be right on

 

Question: Primary control cad cell relay keeps tripping - how can I test it

My primary control keeps tripping the safety because no flame is detected. I have bench checked the ignition transformer(work fine).

Changed the nozzle, checked oil pump is working, when the reset is placed it starts. when the thermostat reaches requested temperature shut down.

Will not start no ignition on next thermostat request. How can I bench test the primary control to see if this is working intermittent. (Dec 19, 2012) Fergus

Oil furnace stopped working...there was a broken knob from the electrical box on the floor. the knob is similar to the one for the oil line. any way that may be the problem. thanks bob (Dec 26, 2012) bob

Reply:

Bob

Watch out:  I'm not sure what's broken but damaged oil burner controls can make the system unsafe. It's time to ask for help from a trained service tech.

RESET SWITCH, CAD CELL RELAY describes how the switch is used, reset, and tested.

Watch out: excessive un-burned oil in the combustion chamber can cause as puffback explosion when ignited.

 

 

Texaco Fuel Chief oil burner won't run, tech says I need new electrical wiring - can I trust him?

I have oil burner (Texaco Fuel Chief) has stopped running. Called person that I used last year, really liked the service job. Called him last week, but now he's retired. Recommended person, so I called for service repair.

Tells me: Honeywell Junction Box has power in but no power out? Said need new junction box?

Well the part cost $500.00 & his install charge would cost about the same. I no longer use boiler for heating house, just for hot water. The expense to remove oil boiler, hire plumber & unexpected cost, I decided to run boiler (hot water on demand).

But now, the price to repair, that's if he diagnois problem correctly? He was to quick diagnoising & didn't comment, boiler needed cleaning. Your information has been very helpful, think I need second opinion, but again

Who? How can I find oil boiler service I can trust to diagnois problem and do repairs correctly. Linda from Kent County, Delaware. 12/6/2014 Linda Calvert

Reply:

Linda, If there is power in to an electrical junction box and no power out that sounds like a wiring or connector error that's pretty easy to fix. Even a regular electrical junction box complete is just a few dollars.

All of the work is the labor.

I suspect that someone is not communicating clearly about the problem and its solution.

If you are uncertain start by calling the service manager at the heating service company and ask politely for a more understandable explanation of what's going on. Keep us posted. - Daniel

 

What do I do if I can't reset the "stack reset button" after running out of oil.

(Jan 25, 2015) brian said:
Stack reset button does not restart the furnace. It buzzes for about 20 seconds. I had ran out of oil, and like before, I bled the lines and hit the reset. Heater started and ran, both flame and blower, for a few minutes, then stopped. Now when I hit reset, it only buzzes. What's wrong?

Reply:

Brian

If you ran out of oil it's possible that the air bleed-out procedure remains incomplete.

If you really have a stack relay and not a cad cell relay as your safety control, see the repair procedures at

STACK RELAY SWITCH

Anonymous said: "Your relay is dead"

...

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 CAD CELL PROTECT O RELAY FAQs-2 - more-recent questions and answers about cad cell control troubleshooting

Or see these

Recommended Articles

• 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

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