Circulator staying on

cbassett

Hi guys,
I just replaced a few parts on my boiler and it seems like it is circulating hot water even when the temp on the thermostat (mercury not digital) is reached. I replaced the Aquastat, expansion tank, pressure release valve and the strainer nut on the pressure reducer. It’s a two zone system and I think it is only happening in one zone. Not sure what to test or how? Any ideas?
thanks in advance for any help.

Jamie Hall

Is this zone valves, or zone pumps? Either way, you need to do some electrical tracing to find out where the pump is getting power from.

cbassett

@Jamie Hall Zone valve. How would I check to see if the thermostat is calling for heat after the temp is reached? We traced most of the wiring on the valves and Aquastat trying to track down another problem so I’m thinking I should start there.

Jamie Hall

Making the possibly unwarranted assumption here that the thermostat controls the zone valve directly... and that the zone valves are of the power open variety (most are).

Start at whichever end is easier and disconnect the thermostat. Keep in mind that a thermostat == at least two terminals of it -- is or behaves like a simple switch. Assuming you start with the thermostat end, if you disconnect the thermostat, that should close the zone valve, just as if you turn the temperature down. If the zone valve stays open -- problem in the wiring. If it closes, problem in the thermostat. If you disconnect the wiring at the zone valve, the zone valve should close. if it doesn't -- zone valve. If it does close, but opens when you reconnect the wiring, either problem in the wiring or the thermostat... and back to the top here!

If the zone valve is controlled through a relay or control box, it's a little more complicated, but the same basic principle.

Keep in mind that there may be power on the wires -- so, as a general principle, turn off the power whenever you make or break a connection.

Dave H_2

What type of zone valve, meaning brand. Pics would also help.

If the zone valve has an endswitch, it could have failed therefor keeping the call to the circulator. it will also depend upon the wiring and controls used as @Jamie Hall said. So matter what the thermostat does, the circ will continue to run

Dave H

cbassett

 Dave H_2
@Jamie Hall
Mdg pic of the zone valve, I actually have replaced the motor on these both in the past but they have always gotten stuck on closed and buzzed when they went out. The yellow wires run through a relay before going to the wall and I’m assuming out to the thermostat, red wires couple and go directly to the aquastat. I’m gonna try disconnecting the thermostat tonight and see what that does. Thanks for the suggestions. 

SuperTech

You should always replace the guts of the zone valve as well as the motor.  If you take the motor off and try to turn the shaft manually it should turn in both directions without any resistance. 
In my opinion just changing the motor is asking for more problems down the road. Been there, done that.

cbassett

@Jamie Hall
Disconnecting the thermostat or switching it to off ( not just turning down the temp setting) turns it off, connecting it back up caused the boiler to fire up and the baseboards to heat back up even though it was 20 degrees above the set temp. So would this indicate that my thermostat has the problem? We painted a few months ago and it got jostled a bit but it still seems level, could I have messed up the calibration on it?

Jamie Hall

Does sound like the thermostat is not quite right. What kind of thermostat is it?

cbassett

@Jamie Hall
it’s a Honeywell 

cbassett

Jamie Hall

The T87N is an all electronic thermostat. Levelling doesn't affect it. However, being all electronic (rather than the old mercury switch type) it will, eventually fail or get badly out of calibration. They are not expensive, and still available -- just replace it.

mikeapolis

In my opinion, that is one of the worst and cheapest t-stats out there. Many issues over the years with those things.

EdTheHeaterMan

if you do replace that thermostat with another T87N, (available from big box, amazon, and other places that the pros use) be sure to change the sub-base (the part on the wall). Dont just put the new thermostat on the old sub-base. As the newer models are manufactured, they make changes in both parts. (same model number but different versions) The problem may be in the part you leave behind.

I learned that the hard way.

cbassett

Thank you all so much for the help. I’m going to try replacing the thermostat and hope that solves it

BillyO

what type of relay is controlling the circulator?

cbassett

@BillyO

It’s an SXT105