Hydronic heating bringing temp above set

Zookeeper33

My family has a duplex built in '68.  Starting at the end of last winter, our heating started raising the temperature of both places 5-6° higher than the temp set on the thermostat.

We have an old GPH Hydronic Gas Heating American Standard furnace.  There are two valve motors - one for upstairs one for down - but both run off of one thermostat downstairs.  Having had this house in the family for 50 years, we know that whatever temp is set downstairs is adequately reflected upstairs.  Because the house is partially underground and encased in concrete, many of the pipes follow exterior walls.  Especially those going to radiators upstairs.

Here is where the problem lies: on moderately cold days (not exactly sure, but maybe above 40°f) the system functions perfectly.  It maintains the temp at exactly the thermostat setting.  When it gets colder, the furnace will run and run bringing the temp way above desired (5-6°f).

I'm currently at a loss as for researching this issue and would prefer to do my own work when possible.  If anybody has any insight into what may be occurring, please let me know.  If you want more details please ask.

Thanks

JUGHNE

This is a boiler not a forced air furnace...right?
What do you have for a thermostat?
And is there any outdoor reset sensor of temp?

Zookeeper33

It is a boiler

We have white and rodgers electronic thermostat: older

As far as I know, there is no outdoor sensor

HVACNUT

Where is the thermostat located?
On an interior wall in a room with, but not above emmiters?

Zookeeper33

Thermostat is located in hallway.  Nowhere near any emiters

JUGHNE

Does the tstat have a cycles per hour (CPH) changeable setting.

Or the most basic item, is the hole in the wall for the wires, plugged so drafts do not hit the tstat?

Zman

I would feel the pipes going to the zones after the call for heat has been over for a while. There is a good chance hot water is "ghosting" past your old valves.

EdTheHeaterMan

From your original comment, the problem started recently (the end of last winter). Think back to the time just before you noticed the problem. Was there any work completed on your home? ANY WORK? even if it is not related to the heating system. New roof?, New Siding?, New Cable wires run?, Work on Electrical or plumbing system?, an exhaust vent for the range or bathroom? Anything?

To give an example, a customer had an addition added to the home that included new insulation. The new insulation also included the attic of the existing home. After the work was done, the heater started to have black soot form. The insulator blocked some air vents that allowed combustion air into the furnace. The homeowner did not tell me about this until a year later when the heater was started for the winter and the problem happened again.

The homeowner did not put the insulation together as the cause of the heater problem. "What does insulation have to do with the heater? The heater is nowhere near the insulation..." As soon as I found the blocked vents and opened them up, the problem was gone. So thinks about what the house was like before the problem and what unrelated things might have been fixed or broken or added or removed just before the problem started.

Another customer had the thermostat mounted on a wall that had the heat pipe for the second floor just behind the drywall. When ever the second floor zone operated the first floor thermostat was heated vy the pipe in the wall behind it. As long as the temperature was mild, there was enough down time for the second floor to allow the first floor to catch up. But when it was very cold outside, the second floor pipe was hot more often than not. So the first floor thermostat did not work (so the customer thought). After replacing the thermostat 2 times and adjusting the heat anticipator several times, I finally was there when the problem was actually happening. The wall where the thermostat is located was warmer than the rest of the walls in the room. We looked in the basement and found the thermostat wire and the 3/4" copper pipe for the second floor were going up the same hole in the basement ceiling/first floor opening.

Two examples of "Things that homeowners wouldn't think of" because "what does that have to do with the problem?"

I hope this helps.

Respectfully Submitted,
Mr. ED

Zookeeper33

Mr. Ed.  Good thinking.

We did reshingle the roof.  But no insulation and the pipes were left intact.  Nothing was moved or altered.  

This issue may coincide with the timing of replacement of the transformer which links the valves down to the boiler.  We woke one morning late last winter to no heat.  Worried about freezing pipes and my parrots I quickly determined the transformer had gone and replaced it.

Zookeeper33

As a response to the other comments:

No the thermostat does not have a cph setting

The thermostat is on an interior wall which is plugged and there are no drafts from there.

As for "ghosting":  the boiler just keeps cycling past intended temp on thermostat so yes both pipes are hot because it is running frequently.



I have also checked thermostats for programmed run times with higher Temps and there are no programs set like that.  

HVACNUT

Is this a cold start boiler?
On the colder days, does one floor get significantly hotter than the other?
You mentioned one thermostat controlling two zone valves. Its possible one or both zone valves are stuck open.
What model zone valves?

With the zone valves, it seems it was once a 2 zone system. 

HomerJSmith

White Rodgers electronic thermostat is battery operated? Model # ?

These tstats may have a jumper on the circuit board that need to be cut when used on a boiler sys rather than a furnace.

Why not replace the thermostat?


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STEVEusaPA

Are you using the boiler to make domestic hot water?