Failed TMV with UFH

12 Nov 2010
Reaction score
United Kingdom
I have a failed Reliance blending valve on my UFH manifold that is still awaiting it's replacement. but the issue is with protecting the screed floor.
I have a Honeywell overheat switch sat on the manifold set at 60* and wired to stop the pump in over temperature condition.
The problem is the boiler pump when heating DHW pumps water around the UFH circuits at 80*.
If I wire the overheat switch into the motorized valve then the UFH will cycle as the circuit water temp falls.
Whats the solution?
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Terrywookfit did you not read the first line of my thread!
The original blender failed
The "like for like replacement valve" was faulty so Reliance are dispatching another with haste (now in my second week of waiting)
The thread relates to protecting the screed and floor covering (tiles & wood etc.) when these valves fault because most people with UFH won't know there is a problem until they burn there feet if there in the house!
In my case the CH water temp from the gas boiler is 55* but 80* when DHW is demanded so I see the fault during this DHW period only, I can control the situation by turning off the UFH whilst the DHW is satisfied until I replace the valve.
People with oil boilers will have this increase in temp and might not react immediately to it, hence the question.
I suppose the answer is to remove the UFH zone valve power only which would allow the boiler to maintain heat to other zones and DHW
TMV's usually fail safe for a good reason.
Two weeks is a Pi$$take.
I suppose you could fit a stat on the flow so the valve closes when there is an excess temperature.
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The UFH blending valves (TMV) are not fail safe!
I asked Reliance technical as there literature states that they are but said it only applies to a open ended water system as in hot water taps or showers etc.
They told me they were sending a valve out out on the day I found the fault (leaking through the splined threads) and when I asked where it was some days later they said they were waiting for the faulty valve to be returned (not what we had agreed) so they were asking me to dismantle the heating system and wait without heat whilst they received it, checked it out then sent out the replacement.
I soon resolved that.
I have a stat on the manifold that stops the UFH pump but the boiler pump still gives flow.

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