room over heating 6-8 degrees over t-stat setting

steveoPirz

I replaced an older "chronotherm" t-stat today with a new digital honeywell t-stat.  Before I changed the t-stat the temperature in the vicinity of the T-stat was rising considerably higher than the 70degree setting on the t-stat.  I thought the t-stat needed replacement.  But the same problem is occuring after the replacement.  This is a single zone house, hot water system with cast iron radiators.  Could the switching relay be malfunctioning?  I need some help with this one.  I have the t-stat set at 70degrees.  but the room is heating up to 76 degrees.  outside temp is 40degrees.

Jamie Hall

Assuming...

that the system does shut down eventually...



First, many of the Honeywell thermostats have a handy dandy llittle icon which shows whether or not they are calling for heat.  Check that first; if the temperature is overshooting like that, but the system is still calling for heat, I would say that the first thing to do is to experiment with different cycles per hour settings and see if you can calm it down that way (on the older thermostat it would have been the anticipator).



If, on the other hand, the thermostat is not calling for heat but the circulators are still running, there's another problem somewhere.  Let us know...

billtwocase

temp

I think the key word here is cast iron radiators. I would suggest lower water temps, and maybe keep the thermostat a couple of degrees lower. If it was a welding switching relay, it would be much more than 7 degrees hotter than what it is set for. You can't beat the heat that you have in my eyes, but it can be radical in warmer weather like we are getting now

steveoPirz

shutdown

the system does shutdown when it reaches the aquastat temp of 180 degrees.  I will try lowering the t-stat temp. and the aquatstat temp @ the boiler. probably to 165.

steveoPirz

shutdown

the system does shutdown when it reaches the aquastat temp of 180 degrees.  I will try lowering the t-stat temp. and the aquatstat temp @ the boiler. probably to 165.

johnhump

t stat

might sound stupid but is the thermostat level if itsd  the kind with the murcury in it it will offset it a couple deg.

JohnHenry_2

I would imagine

it's the high temp in your radiators that's doing that. The boiler will keep producing 180* water until the thermostat stops calling for heat. When that happens you still have 180* radiators putting out heat raising the room temperature.



My old system did what you describe. Older houses with hot water radiator heat are often over radiated. They were designed to have low temp water coming from coal boilers that were continuously lit from October to April.



Turning down the water temp helps a lot. I've found that for my situation, I can heat my house at design temperature to 73* with 125* boiler supply temperature. Of course I can run those low temps as i have a direct vent mod/con, you may not be able to get that low due to issues with condensing flue gas if your boiler isn't designed for it.



What kind of boiler do you have?

Eric_32

Does your

boiler also provide hot water thru a tankless coil or do you have a separate hot water tank?