On 09/11/2026 at 14:04, JohnMo said:

I would take out to middle position see how everything responds, if still not meeting temperature expectations, screw it another turn etc.

Yesterday, the response to fully opening the flow regulator was encouraging. The temperature increased to 40 degrees. The ufh temp stayed at 38- 40 for the rest of the day and it was at 38 degrees at 06.00 this morning. There was a discernable, though small increase in tile temperature.

However, the flow rate had dropped from 1.5 to 1.0. I changed the pump setting from one to two which gave a drop in flow rate. Since then, with the pump set at two, the water temperature has dropped to 34 and now 24 (despite the boiler still having 40 degree water available and heating the radiators efficiently).

The flow rate is now sitting below 0.5 and water temp at 23 degrees.

On 09/11/2026 at 14:04, JohnMo said:

I would take out to middle position see how everything responds, if still not meeting temperature expectations, screw it another turn etc.

At midday it has settled at 30 - 32 degrees with the flow remaining just shy of 1.

I don't understand why adjusting the pump rate had a retrograde effect on the ufh water temperature. Does it indicate component fault?

For a long term, effective and robust solution, I’d change the pump and mixing valve arrangement. This one is very crude, and looks to be quite an old setup too.

These are what I fit if I need a mixing valve:

Note the position of the thermo control head. The boiler can pump to this and bypass back, vs the flow being strangled off.

Also you’ll gain the modulating pump which will adapt to the required duty.

One other thing to rule out is air-locked UFH loops. Was the system flushed or purged through ever?