UFH seems to have a problem

[gritstone76]

I have two adjoining cottages, each with an identical UFH system downstairs. Both been going fine for around five years.

But for the last few weeks, one of the systems doesn't seem to be running most of the time. Essentially the UFH does "work", in that I can turn the thermostat right up, and hot water cycles around. But the issue seems to be that the underfloor temperature probe is returning figures that are higher than expected, and rise very quickly once the system is on. Meaning that the thermostat shuts down the UFH pretty quickly after coming on, and the floor slab doesn't actually heat up as it is supposed to.

I happened to have a replacement (and identical) thermostat here, for another install we're doing, so I tried swapping that out, but no joy - the same very fast rise in floor temperature.

I was wondering how likely it is that the temperature probe itself has failed? Does this ever happen?

I'm also slightly suspicious about the pump (Wilo Yonos)... this does audibly start up and it vibrates during operation, but it doesn't seem to make as loud a "pumping noise" as the pump in the other cottage. But I might be imagining it!

Any other ideas??

Thanks

 

[John.g]

If you can add up the total flowrate by adding up the individual loop flowmeter rates and reading off the manifold flow/return temps ( if thermometers installed) then the output can be calculated which may help.
What mode/setting is the Wilo on?.