Heating Boiler Operating Steps: FAQs

Q&A on the sequence of steps in operation of hydronic heating systems

Heating Boiler Cycle Time FAQs

How Long Should the Oil Boiler's On-Cycle Be when Making Hot Water?

Hi, love this site as a DIY'er. I have a question that I have yet to find asked & answered directly, so here it is along with background info.

I have a Weil Mclain WTGO-4 tankless oil boiler in which I recently replaced the combustion chamber lining & nozzle.

Through the peer hole the flame looks good, no flame-end sparks, no smoke & I can see the new chamber glowing hot during & after the cycle.

With the new chamber, I noticed that my cycle for the domestic hot water only (DHW; tankless coil in the boiler) is fairly quick now, less than a minute, until it reaches set HI temp & cycles off.

Is this okay & efficient? I am assuming the new chamber is contributing to this quick DHW heating cycle but just want to make sure. Thanks for your feedback!

Question for search engines: How long should a oil boiler's domestic hot water (tankless heater) cycle be? On 2022-09-12 by David -

Reply by InspectApedia (mod)

@David,

Watch out: It's possible that you're running the burner too hot which in turn can damage the heater. While I appreciate do it yourselfers and have been one myself, it's the unfortunate truth that it's pretty much impossible to correctly set and tune an oil burner without instruments.

by David - on average 2 minutes to heat the boiler from 160 (LO) to 180 (HI)

@InspectApedia, thanks for your thoughts. I wanted to give an update for future search users.

My DHW (Domestic Hot Water) cycle only (off-season; not winter) seems to have stabilized & it is now taking on average 2 minutes to heat the boiler from 160 (LO) to 180 (HI) (New gauge installed too).

I believe the new combustion chamber has now “cured”.

Hope this helps future DIY’ers who are mechanically inclined & well researched & don’t want to spend excessive fees for ‘Pro’ jobs that can be done (at their own risk of course).

Reply by InspectApedia-911 (mod) - factors affecting oil fired heating boiler "on" cycle time or run length

@David,

How long the boiler will take to heat from LO to HI will vary a lot depending on variables such as:

- Whether or not the heating zone circulator pump(s) are running or not (if running, the burner will take longer to reach its "HI" and shut off)

- The starting temperature of the boiler

- The presence of and use of a tankless coil for making domestic hot water

- The oil burner nozzle size in gph

- The oil burner adjustments for air supply and draft (but beware, if the boiler is running too hot OR too cold that may be unsafe)

What are the draft over the fire and in the breech at your boiler and oil burner?

What is the stacked temperature after 5 minutes or longer?

Followup by David - Draft -0.02 over fire, 0.04 "WC in the breech, Stack Temperature 520F

@InspectApedia-911, thanks for your inquiry. I finished running tests & here are my stats. Using the Bacharach Draft-Rite, I measured the draft over the fire at about -0.02 WC & the draft in the breech at about -0.04 WC.

I measured the stack temperature at 520 F with room temperature at 78 F since the boiler was running over 10 minutes (2 zones circulating) by the time I took the reading.

Note that the heat exchanger was already cleaned using a soot saber before I replaced the combustion chamber.

Please let me know your thoughts & suggestions as time allows. Thanks muchly for your time.

Reply by mod - draft OK, stack temp a bit high

@David,

Those numbers sound reasonable although the stack temperature might be slightly high.

I'm not familiar with the specific brand soot removing flare that you used- I used bushes and a vacuum.

Reader follow up - Stack temperature now 443degF

@InspectApedia , thanks again for replying. If the digital thermostat I used is accurate, then that would mean my stack temperature was around 442 F when considering the room temperature at the time of measurement

I could also downsize the nozzle firing rate but i’d rather not have to play with the air band on the Carlin EZ1 burner & just use what the last tech I ever paid for had set.

The unit was installed back in 1999 so i‘m just keeping it clean & running as best I can with the tools & DIY skills i’ve learned.

Mod reply - Weil Mclain WTGO-4 tankless oil boiler settings - short on-cycle is inefficient on oil boilers

@David,

Remember that a short oil burner firing cycle can be a very inefficient way to use your heating equipment.

That's because on a typical oil fired heating system it can take as much as 5 minutes for it to reach normal operating temperature.

If you're frequently running it in short on-cycles the oil burner efficiency drops and heating cost increases. That's the reason people downfire the nozzle size.

Photo above: the manufacturer has marked the approximate air shutter settings for this oil burner, probably matched to the oil burner nozzle size in gph.

Followup by David

@InspectApedia & InspectApedia-911, thanks for your thoughts & time on my queries earlier. Muchly appreciated. Love you guys!

To continue where we left off regarding inefficiency on short cycling, the last tech back in 2017 used a 1.00 60W nozzle so i’ve been replacing it with the same. The airband on the Carlin burner was also set to reflect. The label on the unit calls for 1.10 60B. Would you recommend downsizing to a 0.90 60W & slightly adjusting the airband to reflect?

Note that the 2 minute on average DHW (Domestic Hot Water) cycle seems to only go on twice an hour to reheat for the LO to HI settings if no hot water is being run.

Reply by mod -

@David,

Now that I understand that the short on cycle is uncommon and only happens when you're not calling for heat but are simply maintaining heat in the boiler I think you would have a hard time downsizing enough to not have a short on cycle.

After all you're only heating the water in the boiler; no cooler water is returning from the heating zones.

I think I would leave it alone.

Followup by David - Heater is now running great!

@InspectApedia-911, thanks again for your thoughts & feedback. The unit is running great. I will leave it as is. I hope this thread helps future inquiries.

Stay well, stay free.

 

Boiler Won't Run or Won't Keep Running FAQs

Canadian hot water boiler heat not hot enough - intermittent failure

I recently bought a large older home with a hot water base board (slant fin / 3 zone) system.

Twice we have a had a problem where we wake up in the morning (both times it was very cold outside) and the house was cold. The gauge showed the temp at 100 degrees, PSI about 7.

Both times I turned the breakers on the unit off (none were blown) and on and the system immediately began heating the water and warming the 3 zones

Do you have any idea what the problem might be and a solution? Thanks very much for any help you can provide. This is in Canada by the way On 2022-02-16 by Mark -

Reply by Moderator - check for oil burner turning off on safety-reset

@Mark,

Typically in Canada, hot water heating systems are set up so that the circulator pump(s) run continuously, 24/7 throughout the heating season.

In that set-up, when the thermostat calls for heat, all it does is turn on the burner to reheat the boiler.

The fact that all 3 of your zones are cold argues against a bad zone valve or bad individual circulator pump.

Once your heating service tech has assured herself that there are not obvious embarrassments like a loose electrical connection at the primary control, circulator(s), or oil or gas burner, then she'll probably look for a burner that's turning off on re-set and being re-set by cycling its power.

The tech might also check that the boiler water temperature sensor that communicates to the aquastat is properly mounted and has good thermal contact at the boiler.

A more thorough step by step series of diagnoses is given at

NO HEAT - BOILER

If that's the case your system may simply need cleaning and adjustment of the oil or gas burner.

Also see CANADIAN vs US BOILER OPERATION - on demand vs continuous heating water circulation

Boiler shuts off after 5-10 seconds

Hello! During the heating season, my boiler will shut off mid-cycle when the call for heat ends (for example, only running 5-10 seconds). This started when we replaced our aquastat with a different model. Is this going to be problematic in the long run?

Is it a setting that can be adjusted? The previous aquastat would allow it to complete its cycle and reach the HI limit (180), even if there's no longer a call for heat. On 2021-12-01 by April -

Reply by Moderator - boiler will shut off mid-cycle when the call for heat ends

@April,

As long as your boiler isn't short-cycling on and off repeatedly during the heating cycle,

then a short on-cycle at the last "ON" cycle before the thermostat is satisfied isn't likely to be a problem. The system is hot and we don't expect to accumulate unburned heating oil in the combustion chamber.

Watch out: But in other conditions, repeated short ON cycles that don't run the burner long enough to get the combustion chamber up to full operating temperature can lead to trouble. By that I mean that there are many short 5-10 second ON cycles in succession.

If the total "on" time for an oil burner is quite brief in any cycle AND if the combustion chamber isn't quite hot from prior burner operation, there's concern that we leave some unburned or incompletely-burned oil in the combustion chamber. In extreme cases that can accumulate as soot by causing rough starts at the next burner on cycle. If that happens too much we could have an oil burner puffback.

Followup by April

@Inspectapedia Com Moderator,

That is very good to know, thank you! It never does it in succession, just randomly about 3-4 times scattered throughout day (that I notice).

I was under the impression that reaching the HI-LIMIT was the only means of ending the cycle, so the whole thing seems odd to me. Boiler works flawlessly, otherwise.

Reply by Moderator

@April,

No, it's also common for the control to turn off the burner when the thermostat is satisfied.

Boiler burner cycles on and off until temperature is set higher at the thermostat

Hello. I have a hydronic oil fired system with a mechanical thermostat and a circulator. I would have liked to know why the oil burner cycles on and off, but once the red lever is pushed beyond 74 degrees Fahrenheit, both the burner and circulator start.

Otherwise, the burner cycles on and off according to the ambient temperature, but the circulator NEVER starts to deliver the hot water to the radiators. What would cause this problem? Why is 74 degrees the only point where both the circulator and oil burner run simultaneously? On 2021-11-26 by TJ -

Reply by Moderator

@TJ,

The aquastat may be wired and set to run the burner and keep the boiler hot for a tankless coil on the boiler.

If you think about it, a room thermostat is not something that works like an accelerator, producing more heat when set to higher temperatures.

Rather it is simply an on-off switch that calls for heat or turns on when the room temperature is below the set temperature on the thermostat

We don't know the country in which you were living and so your heating system may be wired differently.

Although wiring can be different in farther northern countries like Canada, in the US most hydronic heating systems are wired such fit the thermostat turns on the circulator and the aquastat control on the heating boiler turns the burner on when the temperature in the boiler drops.

So you might need to look at the settings on your aquastat to be sure that they are correct.

In the article index on this page you will find an article explaining how to set the aquastat correctly.

by TJ

@Inspectapedia Com Moderator, Thank you for replying. I reside in the U.S. (North East to be specific) and I still didn't understand why the thermostat would normally cycle the oil burner on and off, but the circulator stays off unless the red lever is pushed beyond 74 degrees Fahrenheit.

Why would the circulator stay off even though the oil burner seems to cycle during a call for heat? I noticed this has occurred with variations in the ambient room temperature which was why I became concerned since oil was being burned without the then heated water being transferred into the radiators.

Miscellaneous Boiler Operating FAQs

Is there a Fan in the Flue Vent Connector Between Boiler and Chimney?

Is there a fan or motor in the damper that leads to the chimney? On 2021-02-18 by Mary K -

Reply by Moderator

Mary

Not unless there is a chimney draft problem.

A standard oil-fired heating boiler or furnace uses a barometric damper that operates by air movement
discussed at

DAMPERS & DRAFT REGULATOR TYPES

for a complete list that includes draft regulation on wood, coal, oil, and combination wood-oil fueled boiler and furnaces.

Some, but certainly not all gas or oil fired heating equipment makes use of power-vents or draft inducer fans.

for example see

DRAFT REGULATOR, DAMPER, BOOSTER

Should the water supply to our boiler stay "ON" ?

Hello, thank you for info. Does the incoming cold water from the well supply stay on or is this closed once the system is filled with water? I was not sure if the same water would recirculate. Thanks On 2020-12-15 by Rod -

Reply by mod -

Rod

Presuming that we're talking about a hot water or hydronic heating system, normally the same physical volume of water stays in the boiler and the loop of piping through radiators or baseboards.

That water is heated and circulates through the radiating devices. You don't normally have to add cold water to the system. If your system is frequently adding cold water then it's probably got a leak somewhere that needs to be found and fixed

Do the return pipes on my hot water heat system need to exactly match the feed pipes?

we have a four zone oil boiler. do the return pipes need to match up with the feed (hot) zone pipes? On 2020-11-21 by barbara -

Reply by mod -

Not exactly, Barbara.

For example two or more heating zones or "loops" of piping might merge somewhere before the boiler and then send a single line from that point back to the boiler.

Why is the first water coming out of my cold water faucet hot?

I get extremely hot water out of the cold water tap for several minutes, is this normal ? On 2020-10-31 by Joseph Phillips -

Reply by mod -

Great question, Joseph, thank you.

Causes of hot water coming out of cold water faucet:

I see this phenomenon of hot water coming out of the cold water tap initially quite often when the cold water piping in part of it's routing it was close to a heat source. For example at our lab and office on the second floor of a building the water pipes to a small bathroom originate in the boiler room.

With no water has been run for a time sheet from the boiler has warmed both hot and cold water pipes and the water contents. Once we have run the water for a minute or less we have flushed out the hot water and the water is again cold as normal.

Why don't our hot water heating radiators get hot enough?

Oil fired range running constantly, only a pipe stat fitted to regulate the heat. The radiators get warm 35 to 40 degrees but no hotter "pipe stat set to 60 degrees,any ideas on how to get the radiators hotter?

The circulation pump is on the return side, I have noticed on previous systems that location of the pump can make a significant difference to the heat from the radiators, im wondering if moving the pump to the feed side of the system would make a difference On 2019-12-18 by David -

Reply by mod - suggestions

I would look for an air blockage in the heat distribution lines, and I would look at insulating the distribution pipes where they are not running through areas where you want heat to be released such as in a crawlspace and basement.

See

• AIR BOUND HEAT SYSTEM REPAIR by PUMP
• AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE

Trouble with air in the heating pipes after changing a circulator pump

Hi I changed the circulator pump out on the hydronic boiler an have air in the system im guessing cause the hot water pressure has slowly becoming less an less to the point that I hardly have any hot water pressure throughout the house, How do I fix this I am LOST. Please some one help thank you On 2017-12-11 by mike

Reply by mod - fixing an air bound heating system

Mike,

The air-bound problem is often pretty easy to fix, either by strategic opening of air bleeder valves on upper piping loops or by forcing air out using a pony pump.

Start with the diagnosis and repair steps here AIR-BOUND HEATING SYSTEMS https://inspectapedia.com/heat/Air_Bound_Heating_System.php

Followup by mike - air in heating pipes vs poor hot water flow and banging sounds from hot water system?

thank you so far. so air in the system will make the hot water slow to a trickle out the faucet at the tub all when you turn the hot water on it bangs. so bleeding the air out will fix this problem? thank you 4 your help

Reply by mod - not enough domestic hot water for washing & bathing

Mike,

I've let us mix up different systems.

Air in the closed-system of heating boiler pipes, radiators, baseboards, can prevent or slow the movement of heating water out of the boiler and around the space heating loop.

That would have nothing to do with a weak hot water flow at a faucet or tub.

Weak hot water flow is discussed at

HOT WATER PRESSURE IMPROVEMENT

Banging water pipes are explained (and cured) at

WATER HAMMER NOISE DIAGNOSE & CURE

Banging noises from a hot water heater are explained at

WATER HEATER NOISE DIAGNOSIS, CURE

Will a leak in building water main harm our heating boiler?

I have a leak in my main water line, when I repair it can the boiler still be use or will it get damaged On 2016-02-15 by tony

Reply by mod -

Tony,

If your boiler is a hydronic unit - that is it makes hot water that circulates through baseboards or radiators - it would not normally consume water.

In that circumstance my opinion is that as long as you keep an eye on the system to be sure that it is not leaking (watch for a drop in boiler pressure when the boiler is off or cold) it can be used safely for the few hours needed to replace the water main.

You might shut off the supply valve to the boiler during the repair to make double sure that it doesn't back-drain out the open water pipe. (It shouldn't anyway as there should be a check valve but the check valve could be leaky).

Watch out: DO NOT FORGET to turn the water supply back on to the boiler when the repair is complete. \

If you see boiler pressure dropping below 12 psi when the boiler is cold or if you hear gurgling in the baseboard pipes or if you see steam discharge at the boiler or its TP valve, turn the system off.

In a heating boiler on-cycle, what component turns on the burner?

In your sequence I didn't see what component turns on the burner. And isn't there a gizmatron that proves draft before the burners ignite? (Feb 23, 2014) Tom said:

Reply: the boiler temperature turns on the burner, controlled by the aquastat

Tom: what turns on the burner depends on the heating system type, and in some cases wiring styles between countries;

In the U.S. an oil fired boiler is turned on and off by the aquastat control.

The thermostat starts the circulator; as water temperature returning to the boiler drops it to the cut in temperature the aquastat turns on the boiler.

For a warm air furnace the thermostat turns on the burner, the plenum heats up, and the fan limit turns on the blower.