Short Cycling vs. Normal Pressuretrol operation

Jamie Hall

what you are describing really isn't short cycling in the sense that folks get concerned about it. In a perfect world (oh, right...) the boiler and radiators would be exactly the right size to fill all the piping and then all the radiators at the same time at which the thermostat was happy. The world isn't perfect... however, if this is happening when you are just maintaing a temperature (not recovering from a setback) on a relatively mild day (not like the weather we've been having lately!) it does suggest that maybe the burner is a bit oversized. Oil fired boilers, however, can only be down-fired just so far before you begin to run into other problems. Dunno. Might try a 10% (no more) down fire and see if it works better -- but I doubt that you will gain much, and it it's really cold out someday, might lose a good bit.

On question 2, you'd be surprised how fast steam will condense sometimes!

movin2gas

Short Cycling vs. Normal Pressuretrol operation

I recently took the opportunity of a cracked steam boiler to replace my oil unit with a new Burnham Independence PV. I've recently gotten Dan's book and am wondering about some behavior of the new system:

From a cool state, the burner will fire continuously for 15 minutes or so, the radiators will heat. At a certain point, it will begin a cycle where it will shut off for maybe 2 minutes, then turn back on and fire for 5 minutes. It will continue this cycle until the thermostat stops calling. Is this short cylcing, or the normal operation of the pressuretrol? I'm beginning to suspect that my boiler is oversized, but I want to educate myself before making any accusations.

Some other differences between the old system performance and new:

1. The upstairs now heats more quickly than the downstairs. It used to be the reverse. With the old system, I had achieved a balanced system by getting some cheap adjustable air valves. With the new system, even the radiators with "closed" airvalves are heating full across, causing the upstairs to be about 8 degrees warmer than down. I'm experimenting with a better quality valve in one room.

2. You can hear air vents wooshing and clicking during the "short cycle", shortly after the boiler kicks in, and then again shortly after it cuts out. Is it normal for the vacuum created by the boiler shutting off to cause an audible intake of air? I am surprised at how quickly this happens.

Is there an answer other than oversizing?

Thanks for any advice.

JoeV_2

My brother just bought a house where this was happening. It would trip on pressure every 7-10 minutes. After replacing the leaky vents, he lowered the flame in his boiler via the regulator and now the house heats up with in 15 minutes and the thermostat turns off the boler -not the pressuretrol.

donald@donaldluckenbill.com

joey, how did he lower the flame?

whats a regulator?

thanks

movin2gas

What about the hissing?

Thanks for the advice. I have a gas boiler, so maybe that's worth a shot. Haven't had any mild days since the conversion, so it's hard to tell on that.

The experiment with the better air-valve was interesting. The radiator resisted heating overnight, which was good, but heated all the way across during the morning setback recovery. From what I've read about air valves, this ought not to be possible. This is the type of valve which has a threaded closing mechanism which can be closed tight, unlike the cheap one I replaced. Is it simply being overwhelmed, and the air is finding its way out anyway? It was quiet, unlike the air valves on the rest of the radiators.

nicholas bonham-carter

air VENT

the adjustable air vent can only slow down the arrival of the steam, not cut it off completely. i think if you were able to get your system running as originally installed, you would find it pretty well balanced, with few "hot-spots", so good at radiator selection were the ancients!

this would mean your main air vents near the boiler were working properly, and of adequate capacity. the pressure should be less than 16 ounces, for maximum comfort, economy, and quietness. you may need a vaporstat, and a good low-pressure gauge [gaugestore.com 0-15 oz.]. it may cost you 3 franklins, but would increase the utility of your system. you can see how much fuel you are burning if it takes an extra 15 min. to get the air out at each call for heat x how many times a day?--nbc

JoeV_2

I don't know what he has on his pipetrain, but he was able to reduce the gas flow to lower the flame. He ended up with half a turn lower.

chemeclimber_2

Sir,

I had this same issue with the old boiler I had which was way oversized. I just had a new boiler installed by Steamhead which was correctly sized based on the installed EDR and burner adjusted via a combustion instrument (All done by All Steamed Up) My system can now run all day if I wanted without tripping the pressure switch. I test ran it for more than 3 hours after they installed it. Pressure holds steady to 3inches (oz ?, can't remember the units).

I would recommend the following:
1. Call All Steamed Up if you are in the Maryland Area and have those guys take a look in person. Don't attempt to adjust the burner yourself without being able to measure the combustion for safety reasons and eff. reasons.
2. If not in the Maryland area, have one of these other guys on the Wall come over a take a look. Will be well worth the money.

Take Care