Best way to handle short cycling on boiler

melo

Have a boiler but no money to replace it.

Boiler had baseboard radiators previously but currently they’re standard radiators. Previous boiler guys told me the boiler itself was oversized for the current setup.

so the boiler short cycles sometimes, basically 30 seconds off then on again. It also turns the air damper open and closed during those short cycling situations.

right now the boiler guy had it as the main being set at 2.75ish and the cutoff set to 2 psi I believe. That seems to helped the short cycling a bit.

My question is other then replacing the boiler which can afford, what can be done?

Also do you recommend Hercules boiler cleaner for anything?

Jamie Hall

Not much. Setting the pressures down to something more like where they belong — 1.5 to 2 psig cutoff, 0.5 to 1 prig cutin — will help your system's overall life and may save a little money.

What is an overall cycle like, from thermostat on with everything cold to thermostat off? How long does it take for the boiler to just barely begin to make steam and get steam moving out in the mains? For the radiators to get hot? And is it then that the cycling begins? (If the cycling begins sooner, you need more main venting — maybe a lot more).

In some situations with an otherwise well vented and balanced system, some benefit can be had with a special relay which will force the boiler, once it turns off on pressure, to not restart for a set length of time — for instance, until the radiators being to cool significantly.

109A_5

I would not replace it either.

A few things IMO;

I wonder about the boiler's wiring, with the damper cycling like that. Commonly the thermostat controls the damper, the damper when fully open (via the dampers 'End Switch') controls the burner. The pressuretrol is electrically often on the burner side of the damper.

What make and model boiler do you have ?

If it were my oversized boiler (one method) I would add a delay timer, so once the pressuretrol trips on pressure (system pretty much full of steam) the burner restart is delayed (in minutes) beyond the point of the pressure drop and the pressuretrol resets. To me burning fuel just to build pressure is a waste and needlessly cycling the equipment is also a waste.

Another method is Duty Cycle or PWM (Pulse Width Modulation) control of the burner beyond the obvious Duty Cycle control of the thermostat. Adding a temperature sensor can enhance this method. With this method the burner never runs long enough to build significant pressure.

The difficulty with the timer method (as least the way I see it) there is not a perfect delay timer that is easy to install and works as desired on most any system. And it seems most folks are not really good with electrical stuff in general.

ethicalpaul

"short cycling" to me is a mistaken term to use with a gas atmospheric steam boiler.

The boiler is simply turning off and on the burners based on the pressure of the steam. Short cycling, long cycling, who cares? What is the harm exactly?

But I understand it annoys people who spend a lot of time in the basement looking at the boiler. I have been known to be one of those people too.

An oil burner I can understand a little more. I don't know which yours is.

What is the square ft of steam rating of your boiler? What is the total EDR of your building's radiators?

How is your main venting? As Jamie asked, what is the timing we are talking about here? Is it cycling off before any of the radiators even see steam? That can be addressed usually with better main venting.

I know this is a lot of questions from me and others, but there are lots of variables at play here, it's the way it is.

EBEBRATT-Ed

I would look at the system a little more. How does the system heat? How long to get heat to the radiation from a cold start (boiler warm pipes basement temp).

We need to find out if the system has adequate venting. Lack of venting can cause short cycling even if the boiler is the correct size.

109A_5

I was recently looking at a Slant/Fin boiler's wiring diagram and noticed they have the pressuretrol wired in series with the thermostat and damper control, so in this case the damper would cycle with the pressuretrol cycles.