ectoplasmosis

As mentioned, having two boilers for your kind of heating system is madness. Ditch your 'installers'.

Except they won't be running anywhere near capacity, except for during a few of the coldest days of the year. Our 7kW Vaillant ASHP is practically inaudible day to day; the only way of knowing whether it's running or not is to feel for the airflow. It's MUCH quieter than the neighbours' gas combi boilers.

If you get the wireless version, then you can stick that anywhere you like, even move it around depending on how you use the house.

“Thermost.” would be equivalent to Expanded I would have thought. You would need to have the VRC700 in a habitable space however; the temp sensor wouldn’t be doing much stuck in a utility cupboard.

Done

You have access to the exact same settings on your VRC700 already: “Room Temp Mod”.

On the SensoCOMFORT controller, just configure the ‘room influence’ setting to ‘Expanded’. This will switch off all circulation pumps once the internal temp reaches your chosen set point. We ran like this during the summer, then switched to ‘Disabled’ mode once the heating season started, which enables pure weather compensation with the circulation pumps constantly running.

That insulation product won't be doing much of anything I'm afraid. With your current plan, it will be very expensive to heat the room. What is the current ceiling height? Could you add 100mm PIR insulation underneath the electric mat? If not, then as mentioned above, an air-to-air split heat pump system will be much more effective and cheaper to run.

50degC design temp is too high, you should be aiming for a maximum of 45degC. Our MCS heat loss calculation document and associated emitter schedule had radiator Watt/BTU ratings listed at Delta-T 50 for ease of comparison to manufacturer's specs.

No, we looked at the Cortizo 20 sliding doors as part of an extension/retrofit. Visited a couple of installations and I wasn't impressed with the design. They look great though! Ended up with Velfac casement doors and opening picture window. Seals are very good. I've attached a pic.

I can't advise on installers, but having experienced the actual product (sliding doors with 20mm sight lines), I was not impressed with the design. Thermal bridges everywhere, sub-optimal seals and a poor threshold design which leaks air.

Everything is plumbed as a single open zone right now, single Vaillant controller running in pure weather comp mode, no buffer/volumiser/low loss header. Rads have been balanced. There is however a stat on the bathroom UFH loop set to close the loop if the temp in the bathroom reaches above 25degC, as there’s a large dual fuel towel rad in there as well, but the bathroom loop is tiny.

Thanks again. The entire system is new, and has been designed around a 45deg max flow temp at -3deg OAT. If I were to remove the blending valve and secondary pump, then run the whole lot as a single zone at the same flow temp, would this work well?

Thanks. If I set the Reliance thermostatic mixer valve to 55degC, which the flow temp will never reach, will this act as if the mixer doesn't exist? Or is the best approach in terms of efficiency to physically delete the mixer and secondary pump?

I have just renovated a Victorian semi, and fitted a Zehnder CA 155 WM MVHR unit. I'm looking to upgrade the standard 'G3' grade filters, but can't find anything finer than G4 for the CA 155 model. Would upgraded filters from any other model fit? If not, is there a way of modifying/making custom filters? My daughter and I have asthma, so it would be great to fit F7 grade or better filters to deal with PM1 particles.