Nickfromwales

Hi mate. To give you a reality check, this sounds like way too steep a learning curve, in too short a space of time, on an extremely fragile budget (being polite there btw). As above, £160k will get you the keys to a house you can just walk in to and put your toothbrush in the holder, switch the telly on, and open a beer. So, question has to be; “Why not take this simple route vs the leap into the unknown”?

Night and day different for your setup then.

Was the 13kw of solar removed and refitted? Eg you’re not adding to or upgrading the solar setup that you have the FiT payments for?

It does (can) if the WC’s are sharing the balanced feed from the UVC multi block aka control group (PRedV). If the cold mains isn’t great, then I always recommend feeding the WC’s off the raw cold main, before any pressure reducing gets done.

I’d have done it for £20 less. 👍. “£20 is £20” 🤣

Meaning the QS was a cock.

Yes, my point is relevant to the OP who hasn't installed a RS appliance.

The only elephant I see, is if the airflow out of the WBS is in excess of the power / flow of the fan in the MVHR unit, then there is a strong likelihood that 'smells' from bathrooms / kitchens 'could' make their way into the room that the WBS is in, but the stink from the WBS would probably overwhelm that anyways. Seems kinda moot now anyways as the OP has installed the kit and is 'happy'. The likely natural infiltration of this dwelling probably renders everything commented on above a complete waste of time anyways, as MVHR has no place in anything other than an airtight structure of 1.0 ACH or less.........

Steel fitters are lazy if you've got lots of 3 and 4 layers overlapping? Time to cut accordingly and do it properly.

You need a full solar survey done BEFORE going even one step further. Any reputable solar company will usually do this for free to try and get your business. Start there, and post the findings here for us to offer any further (accurate) advice

AKA, "overthinking it" lol. 2x 50mm pipes to 2x 50mm AAV's is more than adequate. Usually these runs aren't much more than 10-15m max, and I've shown these working (to the BCO's) and they've been happy that they function so 'tick that box'. Step away from the scientific calculator

Always a good time to see if the downstairs ceilings stand any chance lol

The seat / face of where the rubber seal presses against, so on the trap, then put the rubber on, the seal again atop. You can’t go twisting these around or the rubber gets ejected. Take a bit of practice but always gets the results I need; 100’s of showers / wet rooms done over the last couple of decades (+) and not a single complaint or leak.

You don’t have a choice! Either you go up or a plumber does, but if you don’t do as above then your system will stay airlocked and you’ll have just wasted time and money / chemicals for zilch. Some installers used to invert a pipe to a manual vent in the head of the attic space, so this can be vented (bled of air) without going on the roof. If you have bottle gents then you’re prob still going up as these cook and fail and are usually isolated by the installer with a valve so they don’t get called back when they leak (which they will do, so you’ll need to change those too most prob). This isn’t an afternoon job for DIY.

+1. This needs to have an airtightness test done, and a score recorded, before moving an inch further with this