Temperature in Room too High- Thermostat Issue?

[frank1492]

I am back with a different themostat question. I am trying to figure out why sometimes the temperature at the thermostat (and thus in the house- single zone system) gets too high. I just got a new digital thermostat and the condition persists. Diagnosis is made more difficult because the condition exists in my GF's house and I am only there periodically. The house has an oil burner, hydronic heat and a 24VAC control system (2-wire). The other night she claims to have come home and found the setpoint at 65 when the actual temp was 70, and she claims there was heat in the radiators. She also says the oil burner was running at the time, but I told her that might be misleading since heat emission is largely controlled by the circulators and the burner might simply be needing to raise the temperature of the hot tap water. (Note: This is in the NE where the temperature all day has been in the

40's.) I can't supply other details except that she says sometimes this happens, sometimes it doesn't. Also she claims she can "always get the heat to stop if she manually resets the setpoint." (Don't know quite how to interpret that.) The only thing I can think of is that there must be a problem with the oil burner control module, perhaps a sticky relay. Your thoughts? Let me know if further information is needed. Thank you. Frank

[frank1492]

Could something be causing the circulators to stay on too long, or not operate independently? The problem seems worse as the outdoor temp increases. She had a new burner installed a few years ago, don't remember complaints before then.

[Ed Pawlowski]

I suspect the circulator circuit may have a problem. The relay that turns them on and off may be sticking in the "on" position.

There is also a valve in the system that will allow gravity to circulate the water if it is opened. It should be up near the ceiling and probably has a thumb screw on top of it.

[frank1492]

This is a White-Rodgers thermostat. There was a jumper wire that was to be cut for hydronic systems which I did. I believe that lengthened the cycles somewhat. There was also a heat anticipator jumper which was to be clipped to disable the anticipator, which I didn't clip. Should I try doing that? That will of course turn the heat on a little sooner, but I would think it would have no effect on shutting off the heat too late (her problem.)

all rooms in multistory dwellings receive equal heat.

hour. It's the digital version of the heat anticipator found on older mercury bulb stats. Cycles per hour/firing rate is different for gas or oil, forced air or hot water, high eff furnaces, etc.

[frank1492]

I will examine your first choice, but the second is interesting. I would think that if gravity were allowed to circulate the water under certain ambient room temps (perhaps caused by daytime warming) that too much heat could be released from the registers. Therefore closing this valve would make the heat emission more precisely correlate with circulator action, which is what I would want. (Is this correct?) Assuming I can find the valve when I go down next, how do I adjust the screw to completely shut off gravity circulation?

[frank1492]

This is a new thermostat (White-Rodgers) which replaced a Honeywell. Both are digital. The Honeywell was replaced because of this problem, and the same conditions occur with the new one, so rule out the thermostat. I will follow your suggestions. Thanks.

[bud--]

An anticipator turns the tharmostat off early to account for the heat that is in the system. For hot water that is the hot water that is in the radiators. Before digital, the anticipator was a small heater that heated the thermostat when heat was on to cause it to open early. Hydronic has more heat stored in the system when the thermostat opens than hot air. If the thermostat does not open early enough the heat will overshoot.

Possibility the hydronic jumper should not have been cut?

Link to thermostat information?

I assume your system is not zoned.

I would reread the thermostat manual. Also the burner manual. Then check if the burner follows the thermostat. That was easy with the old thermostats, but you don't really know what the digital ones are doing. There may be time delays in the thermostat and the burner control.

My system the circulator and burner both turn off when the thermostat opens. Does the your circulator turn off, run on a time delay, run continuously?

My system, installed in the 1920s, was probably originally gravity with a circulator that was probably added. It never had a valve to allow gravity operation after the circulator was added (sounds like a useful feature).

[ckozicki]

e that all rooms in multistory dwellings receive equal heat.

s per hour. It's the digital version of the heat anticipator found on olde= r mercury bulb stats. Cycles per hour/firing rate is different for gas or = oil, forced air or hot water, high eff furnaces, etc.

and this is something you might need your boiler service contractor t= o check, is to check your boiler's min and max water temps. These settings= are probably inside a box on the boiler itself. Typical HI =3D 180 and ty= pical LO =3D 120-130. YMMV, but too high a Max setting(200F or over) will n= ot only guarantee an overshoot as in your case but can cause bleedoff into = your overflow mechanism.

We're all just throwing stuff at this here, Frank, hopefully something will= prove the right answer. Until then it's just "stump the chumps". LOL!

-CC

[Stormin Mormon]

A couple friends of mine had a similar moment, except they were on the 4th thermostat, not the 2nd. Turned out that a relay on the furnace had been sticking. I was able to troubleshoot, diagnostic. Find the sticky relay, and replace.

In this case, long magnet tip nut setters were needed. And some skill in wiring, and troubleshooting.

Christopher A. Young Learn more about Jesus

.

But given the overall picture, I'd say that whatever the thermostat is controlling at the other end is having a problem. And I'd try to figure it out fast, as if that is what it is, next time it might not shut off at all.

[frank1492]

Thank you all for your time and expertise helping me with this. I will employ your ideas this weekend and have more data to report. I hope some of the simpler possible causes exist, otherwise the service guy will have to get called, and given the more complicated possibilities, that really worries me!!!!

[RBM]

From your description, it sounds like a very basic hydronic system with a domestic hot water coil. The only parts of that system that could cause overheating would be a faulty thermostat, which was pretty much ruled out, possible sticking circulator relay, although doubtful, an intermittent shunt on the thermostat cable. If it's a very old cloth wrapped cable with cloth wrapped conductors, this is a pretty good possibility. The last possibility would be an open flow check valve. Crank the valve closed, then open it one turn.

[Stormin Mormon]

The challenge is to be there at the moment when the problem occurs, and then to find the problem.

Sticking relay, and thermostat wire insullation rubbed through sound like good places to start.

Christopher A. Young Learn more about Jesus

.

[frank1492]

Sticky relay and open flow check are high on my list! (The thermostat wire is plastic coated.)

[frank1492]

Yes, this does seem intermittent. When she got home from work tonight she said everything was fine.

[frank1492]

Followup note: The burner and the circulator turned on tonight when the temp and setpoint in the room were the same. After the burner shut off the circulator continued to run by 3-5 minutes. The actual temp was then one degree above the setpoint. So far I have never seen the burner run without the circulator, but there may not be enough observations. Will continue to post periodically. If this were true all the time we would have something. Comments welcome. (Thanks.)

[Stormin Mormon]

My friend, I think you're right. You're well on the way to figuring it out. You can expect HeBe-ub to give you grief, now. Read the "who is it" thread to understand why.

Christopher A. Young Learn more about Jesus

.

[trader4]

If it worked as you describe all the time, I'd say that the heat anticipator setting on the thermostat could be the problem. The thermostat turned on when the temp shown was the same as the setpoint. Internally the thermostat likely knows the temp is actually 1/2 deg or so lower and so it calls for heat.

IT shuts off when the temp has risen enough, to say setpoint plus some margin. Then the carryover heat continues raising the temp and the thermostat now shows the setpoint +1 deg. Adjusting the heat anticipator or swing setting in the thermostat could reduce the upswing.

Bottom line, the above sounds like a system that is working, but could use adjustment. It's very different than the other reports of the system continuing to run and taking the room temp 5 degs above the setpoint. If those huge overshoots are still occuring, and have occured with 2 thermostats, then you have a problem and it's not the thermostat or thermostat adjustment.

[frank1492]

There are two swing settings on the W-R, jumper selectable. As per their instructions I have the setting at 1.7 degrees for baseboard. (For hot air they recommmend 1.) The heat anticipator is not continuously variable but is jumper selectable. It is currently set to anticipate. My GF has been instructed to note carefully when a gross overshoot next occurs, to note the thermostat readings, and to check to see if the circulator is running. When she next logs this, I will report back.

[frank1492]

Do you mean "Hey Bub?"

[Stormin Mormon]

That (as you stated) is his user name. As I stated, is a reflection of his attributes.