Steam Pressure Short Cycle

radmix

A quick question about a steam boiler installation. New installation boiler runs fine with no problems until the customer sets the Thermostat back at night. In the morning the boiler will have long run cycle to come back from a setback. The pressuretrol will shut the boiler down when the pressure reaches 2 Lbs the pressure will drop in 2 minutes to restart the boiler. The boiler only takes 2 minutes to reach the 2 Lbs and the cycle repeats itself. This continues until the Thermostat reaches its target temp. According to the customer it runs on 2 minute cycles only on long run cycles The pressuretrol is set all the way down to .5 and the differential is at 1 pound. Is this normal

Jamie Hall

Perfectly normal

Most steam boilers are slightly oversize -- for various reasons.  What is happening is that on the long recovery, all the radiators finally get to the point where they are condensing all the steam they possibly can, and all the steam lines are as hot as they are going to be -- and the condensing capacity isn't quite up to the tea kettle in the basement.  At which point the pressure will rise and the pressuretrol will shut things off until the radiation can catch up to the boiler.  At which point the pressure drops, the boiler fires up again, and off you go.  It's all working exactly as it is supposed to.  I might add that the cycle times quoted are about normal.



Until the thermostat is satisfied.



I am not, personally, at all convinced that setbacks deep enough to get a properly sized boiler to cycle on pressure save any fuel at all, but there is a good deal of debate on that subject -- and it is very difficult to prove it one way or the other.  3 degree setback?  Probably fine.  6 or 8 degree setback?  Probably wasting fuel in recovery.

Si_zim

Seems normal

Yes - this is about where I am with my system also. Everything performing very well except shortcycling on recovery from setbacks - and the fact that every vent I try is too noisy since I am a very light sleeper. We like a temperature of about 65 while sleeping but the 5 degree bump up in the morning is enough for a good period of short cycling (and some hissing)

radmix

Short cycle

 Thank You for the replys.

Joe V_2

consider this too

As I am finding out. With this cold snap, my boiler started short cycling while trying to satisfy tstat from a four degree setback. Also, two radiators suddenly feel merely warm unlike the rest of them, which are hot. Radiator steam traps flaking out ? likely. But with the two largest rads out, boiler becomes oversized.