Underfloor heating help

[querquelatunae]

Hello all,

Having recently moved house, we've just changed our old unreliable boiler and vented hot water tank system for a Viessman 100 combi.

We have radiators upstairs and a few downstairs - all now getting much better heat through them. We also have two wet underfloor 'zones' downstairs. The three circuits are separate and controlled by new Tado thermostats.

The underfloor system has two switches:
1. Drayton zone valve actuator - set at position A
2. Wilo pump - the plumber has set it at the 'fixed' (rather than variable flow, which the manual seems to suggest is for underfloor systems) at max speed 6.
Plus, it also has a radiator style thermostat knob on the pipe to control the heat?

These were both here before the heating system change, but I'm sure were in a different position. So far, the smart meter seems to suggest that our underfloor heating is quite expensive, despite being on low and not very often!

Any tips and suggestions very welcome! Have been in poorly heated houses for a long time, so would be good to get to grips with the system!!

 

[Exedon]

Some clear pictures of what you have would be useful
Plus ask for this to be moved to Plumbing and heating forum.

 

[MeldrewsMate]

I suspect your 'radiator knob' is the setting for the floor temperature, if your floor temperature is higher than necessary then more fuel will be used to keep it at that temperature. Refer to the design documents, if not available set it so the flow into the floor is 40-45C.
Do you have flow indicators on the UFH manifold? Lower the pump speed until the first indicator drops lower than maximum.
The zone valve will probably be controlled from a controller and will be open when either or both thermostats call for heat.

These are just initial values and should be tuned by someone who knows what to do and is familiar with your system...the system designer.

As for your bills, all are relative, though running UFH 'not very often' can be uneconomical because the large thermal mass of the floor must be heated and this can take several hours from cold.
The above assumes UFH set into screed with at least 100mm of insulation under it. UFH set under an uninsulated suspended floor will not be economical to run.