I have a radiant heating system with hot water boiler. I have 4 zones and all thermostats are set to 20c. The temperature, however, goes to 28c and stays there. I have tried few things; put new batteries in my digital thermostats, replaced my digital thermostats to manual thermostat, replaced one of the honeywell zone valve. But, I still have the problem. Any idea what I need to do? Do I check the wiring around the zone valves, replace the remaining zone values, bleed the system?

 

Do the thermostats click off? Can you hear a click when the temp goes above 20? If so, when the thermostat is satisfied does the boiler continue to run? if not, do the pumps continue? Do you have a zone valve controller?

 

How is your radiant arranged? Is it tubing embedded in a a massive concrete slab or some other arrangement? If a slab I suspect it is simply overshoot due to the slow response time of the slab to the air temperature.

 

Yes, I have 4 zone valves, they all are set to 20c, 3 are digital and 1 is manual. I can definitely hear a click when the manual one goes over 20c. I replaced digital with manual for testing, and they clicked too. All zone valve indicate that there is enough heat, they show pressure. But, the boiler continues to start every 10mins and stop after around 2mins. The PILOT, tank and 1 zone value were replaced last year, but the problem is not resolved. I don't really know how the radiant is arranged, whether the tubing is under a concrete slab. Can I get any other information that could help?

 

Two things come to mind quickly. Too high of temperature if you have slab heat or ghost flows. That is migratory heat when you don't want it somehow. I have seen heat move up the return lines. Verify the pipes cool off between calls somewhat.

 

Since you mention that the boiler comes on every 10 minutes and runs for 2 is this the burner coming on and off? The boiler may be getting a heat call causing hot water into zones.Try shutting power off to boiler as soon as the thermostats have brought rooms up to set temperature.This should tell you if the stored heat is causing the over shoot.

 

I noticed that too Saves...

Spuser, let me ask this:

How long have you lived with this system? Do you have any history with this boiler?

Do you know for a fact that this boiler has not behaved like this for long time?

What is causing the boiler to start and stop? THAT is the question!

What do you mean "they show pressure" ? Please explain...

Let's back up a bit here:

What is the make/model of your boiler?

What is the make/model of the operating aquastat on the boiler?

 

Ok. I am going to try to answer all the questions here and will get back on what I don't have yet or any new ones.
I moved here 5 years ago, heating was perfect for the first 3 years, this problem started 2 years ago. I called Sears Engineer immediately and they replaced 'Gas Valve' and 'Thermo couple', and they recommended replacing 'Expansion Tank' and 'Air Value' soon. Since their fix didn't resolve the issue, next winter I called another company who replaced the 'Expansion Tank' (cylendrical tank) and 1 zone value to my main floor living room. The other 3 zone valves are 1 in the basement, and 2 in the two bedroom upstairs. I haven't got the 'Air Value' replaced yet.
By "they show pressure", I meant that when I push the lever which is under the zone value, I can feel pressure and I have to push hard. When the room temperature go below what I have set, then (the zone valve opens and) the lever moves very freely.
The system is TELEDYNE LAARS Mini-Therm II, I will get more details on make/model and meter readings tomorrow; i think the dial reads 130ish in one place and 11ish in another, but i will get more info tomorrow.
--
If I turn-off the switch to the boiler right after the temperature has gone over what I had set, the floor starts cooling off immediately and I have to turn it back on after a couple of hours.
I timed the boiler start/stop today... burner/fire starts every 6 minutes and says on for 1 1/2 mins, so between a stop and next start it's only 4 1/2 mins. The duration between each start and stop is so small that I can't figure out if the floor is cooling during that time. However, in my case the temperature is already upto 28c when I have set it to only 20c; it is definitely not cooling down to 20c during that 4 1/2 (or 6)mins. By the way, the maximum temperature it reaches seem to be 28c, and then it stays at that until I end up turning the boiler switch off.
--

 

Since the house starts to cool off immediately it is a control problem, thermostats, zone valves. When a thermostat calls for heat it applies power to the zone valve motor and that is when that valve leaver becomes lose.There is an end switch in the valve which is closed mechanical when valve is fully open.This switch tells the boiler control that there is a heat demand which will start the circulatory pump and when the boiler water cools enough the burner will come on until it reaches the high limit or the call for heat is lost.I would check for sticking zone valve, lose wire connections,intermittent end switch and incorrect wiring of the new zone valve.

 

What brand and model thermostat are you using?

 

I'm thinking that those don't have an 'aquastat' ... just a wiring box on the front... and inside that box there is a temperature dial... if I recall correctly... and the wires from the zone valves connect to terminals on the left side of the wiring box?

While it would be possible for the new zone valve to have been wired wrong, I believe you said that problem started a year before the valve was changed, is that right?

 

And it does this constantly? 24/7 as long as the boiler is turned on?

It was doing this while the techs were there to observe?

And they didn't think that was at all odd?

Then took your money and left?