Hydronic floor heating--room never changes temp

Mark Eatherton1

a leak below the slab. Feel the make up connection.If its cold, you need Leak Busters!

ME

Dave Johnson

Room with Hydronic Heat--Never changes temp

We've noticed our family room (concrete slab with hydronic running through the slab) never changes temperature. We have had the the thermostat set to 50 for 3 weeks and the room and floor have stayed at a constant 72. We've noticed rather high oil consumption rate and are concerned that the hydronic floor is responsible--i.e., it's always calling for heat.

I've done the following checks: adjusting the thermostat up (to 80 or 90) does indeed cause the hot water circulation pump to start. Turning it back down to 50 turns that pump off. I can hear the zone valve actuate, but there is no positive indicator that it is fully open or closed. If anything, the zone valve sounds different (shorter noise upon closing) than other zone valves for different areas of the house.

The only other thing that distinguishes the radiant floor heating zone from the rest of the house (baseboard) is that after the zone valve is some sort of elbow/T--one leg of which returns to the boiler.

Any other checks I can perform?

Mike T., Swampeast MO

With the t-stat down and the circulator off for a good period of time feel the lines leading to and coming from the floor. Both should be quite cool. Feel on both sides of the tee you see connecting to the boiler AFTER that zone valve.

If both are warm you have flow.

The tee you describe sounds like part of some bypass--probably to reduce water temperature to the radiant floor zone.

If you're getting flow the zone valve may be bad and the other circulators in the system are providing some circulation. It's also possible (I guess) that the bypass arrangment could be improper and you are getting flow through it even if the zone valve is working properly.

Of course copper is a good conductor of heat but if the distances between the components are fairly large you may be able to find what is at fault (be it a device or unintended operation) by feeling or measuring temperatures.

Radiant Wizard

Check this out

If the pumps not running water's not flowing. Sounds like this system is running on a fixed water temp. Here's my take.

System is running at design conditions throughout the heating season. Slab comes up to temp at night and zone shuts down in AM. You still have mass retaining heat so our friend the sun starts shining on in. That along with the slow displacement of heat from the slab keep the room warm. Now when our friend the sun goes to sleep and the room temp drops below setpoint, the pump starts again and the cycle continues. Sounds like the problem is the control strategy. You yourself said the pump stops.