Nickfromwales

Yup. Open 100% or shut 100%.

No. They're serving two separate bodies of water with dissimilar hydraulic resistances. The manifold pump see's high and low resistance as a constant operating environment due to loops opening / closing in varying numbers at varying times. The ASHP circulation pump must see a constant in order to satisfy the mandatory ( factory fitted / supplied in most instances ) flow switch, which tells the heat pump that all is well and it can fire up safe in the knowledge that the flow rate is sufficient to convey the produced heat away effectively.

I've spotted why TRV = Thermostatic Radiator Valve ( big white knob with graduated numbers on it ) typically found on the end of a domestic radiator TMV / TBV = Thermostatic Mixing / Blending Valve ( the valve that mixes flow and return ( hot and cool water )) together to reduce the delivered water temp

Welcome, and nice avatar lol.

The FMU3 is ample tbh. The combination control group is a bit OTT imo, but it is a relatively neat solution too. Ultimately you can do all this 'conventionally' and spend a bit less, depending on how you want to control the rads eg rads linear to heat requirement via TRV's on the rads, or ON / OFF via room stats and manifold actuators. In bedrooms I think I'd still prefer TRV's in each room, so maybe consider 'smart' TRV's from a control package supplier that does the whole family of products as a finished system solution. The biggest focus here should be on room stats with at most a 0.5oC hysteresis so you then don't actually need W-Comp. I've fitted Vailllants W-Comp and it was a huge ball-ache with many return visits to try and get it to work nicely. Ended up removing it IIRC and just going back to the boiler stat vs TRV's which worked perfectly well ( client simply turned the boiler temp up slightly in the bitter part of the winter and vice / versa ). I 'recently' fitted the Honeywell EVO system and am quite impressed with the range of products and the simplistic stat-per-zone for temps plus a central hub for the 'thinking' side of things. Pretty much plug and play so a nice easy handover If you're feeding everything from a buffer ( have you already spec'd and bought this, and what is heating this and to what stored temp ? ) then you'll need one tapping for rads and another for UFH, ideally with a 2-port zone valve on each leg. Pointless in having the extremely expensive M3V in this instance, as the secondary manifold will deffo need its own pump ( as you're going to be hydraulically separated from the pump of the heat source because of the buffer ). The images shown in the Emmetti literature expect a 6m pump to be on the primary side of the UFH manifold to force water around those loops, and you'll be missing that unless you buy and install it. Personally I'd try and do away with the second primary pump and just use pumps on manifolds to feed both rads and UFH as these should pull heated water from the buffer without any further help ( as long as they are on separate tappings or Tee'd off away from each other immediately at the buffer ( eg with a 28mm x 22mm x 22mm tee ). Also, Vaillant stated that they did not have a W-Comp solution for 2x heating circuits + DHW eg triple S-Plan but that was a few years back.

No. It’s a safety thing full stop. Forget modulation, it’s to prevent the max heat delivery ever getting into the slab. Not any old TRV, as these have capillary wires coming off them which go to a reference sensor probe ( look at the pics for the curly silver wire ) so must be made fit for purpose. Regular TRV’s reference room temp to actuate, these take reference from the probe. No. The manifold pump is there for circulation of the water through the loops. The ASHP pump is there to circulate heat back and forth the manifold > ASHP only and should never be relied upon for UFH flow. Yup. Not quite 100% but the majority of it. No. The flow to the manifold from the ASHP will be arrested by a 2-port zone valve fitted before the manifold in the flow pipe. With that shut you can run the manifold pump to do as per Jeremy did and Bobs your uncle and Fannys your aunt. 👍 Water will always follow the path of least resistance, so the pump will just happily recirculate through the pump / blending set arrangement. The answer is, you need a manifold pump and blending set ( TMV ) full stop. Convincing yourself that the risk is minimal is academic as you can still get that small HP over 50oC, regardless of how long it takes to get there. Scenario could be that just one loop is open and flowing vs the load of the entire heated area, so compound failures are what drives these initiatives, guidelines and regulations. No shoot off and buy your TMV 😎!!

Has this passed B-Regs on such low volume airflow from the bathrooms? I only fit a single run for an extract if it's a cloakroom and less than a few metres to the plant / manifold. Every single bathroom has always had; double runs to a single valve, or two independent runs to two separate valves in the same room ( for a larger bathroom ) and same for kitchens ( dual or split dual ). Makes things a LOT quieter on boost too.

Don't forget the insect / vermin stainless mesh under that additional external insulation

I'd add a vertical rip of 25mm thick PIR at the screed perimeter too, so you're less exposed at the periphery of the heated floor, eg so just the plasterboard sits atop the screed, rather than the service batten & plasterboard.

Just use joint profiles like these and leave the router alone! 12mm is very little meat to be cutting into.

Tell them you'll pay when you're happy and not a second before.

Should have tidied up before the photos tbh, that looks like a shithole.

Struggling to find anything to dislike there, and I looked twice Really nice touch with the RAL heads and cills in the outside window & door reveals, have noted ( stolen ) that for future brownie points. Really liking the study / office at the back of the landing space. Architect input or your own ideas mostly?

+1. Got me out of the shit a good few times. You'll need some elbow grease though. Best is to do this literally two tiles at a time or you'll be filling yourself with false hope ( as you're probably aware it's nigh-on impossible to tell good from bad when wet ).

...and finally, the last three digits on the back of your card please.