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Piwoslaw · 01-31-11, 02:09 AM

It appears that boilers are prone to short cycling

After moving into my wife's house I noticed that the gas boiler was cycling on and off 2-3 times per minute! The water temperature was set to minimum and it appears that the heat radiation from the flame just after start-up was enough to trigger the aquastat. Setting the water temp a bit above minimum solved the problem. Adding a thermostat in the house also helped.

Cholcombe, just to make sure I understand your setup: You have an aquastat that governs the water temperature and a thermostat somewhere in the house that turns the boiler on/off depending on room temperature? This is how it should be and the best thing to do is to set your aquastat higher. This will make the radiators hotter, but the thermostat will make sure the house doesn't overheat. Also, maybe you can increase the tolerance on the thermostat, say from 1°F to 2°F?

Three more things to try (if possible):

Make sure you don't have air pockets trapped in the radiators, or elsewhere in the system (parts of the system, like one end of a radiator, would be colder than others),
Clean out the inline water filters,
Speed up/slow down the water circulation pump.

New boilers and furnaces reduce the flame size as the return temperature approaches the set limit, but I understand that your old burner doesn't have that capability. I would advise you to buy a new boiler, maybe slightly smaller, since that would be oh-so-much-more efficient, or ask a technicial if your boiler can be retrofitted to be more efficient, but since it is to be replaced shortly then there's no sense in spending $$$.

01-31-11, 02:09 AM	#3
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	It appears that boilers are prone to short cycling After moving into my wife's house I noticed that the gas boiler was cycling on and off 2-3 times per minute! The water temperature was set to minimum and it appears that the heat radiation from the flame just after start-up was enough to trigger the aquastat. Setting the water temp a bit above minimum solved the problem. Adding a thermostat in the house also helped. Cholcombe, just to make sure I understand your setup: You have an aquastat that governs the water temperature and a thermostat somewhere in the house that turns the boiler on/off depending on room temperature? This is how it should be and the best thing to do is to set your aquastat higher. This will make the radiators hotter, but the thermostat will make sure the house doesn't overheat. Also, maybe you can increase the tolerance on the thermostat, say from 1°F to 2°F? Three more things to try (if possible): Make sure you don't have air pockets trapped in the radiators, or elsewhere in the system (parts of the system, like one end of a radiator, would be colder than others), Clean out the inline water filters, Speed up/slow down the water circulation pump. New boilers and furnaces reduce the flame size as the return temperature approaches the set limit, but I understand that your old burner doesn't have that capability. I would advise you to buy a new boiler, maybe slightly smaller, since that would be oh-so-much-more efficient, or ask a technicial if your boiler can be retrofitted to be more efficient, but since it is to be replaced shortly then there's no sense in spending $$$. __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.