Nickfromwales

Easily dismissed, but I accept the caution here. If your MVHR is sucking in cold air over the winter, and you bought a half-decent MVHR unit, then the 1kw pulse-heater will be going most of the time. This uses direct electricity on demand. If the ASHP is providing space heating regardless, then why would you not use that (very cost-effective) source of heat energy to off-set the cold incoming air temp?

Or that you do less plumbing than me, lol.

Nope. I used glycol in a system I installed for a client in Oxon. Zero issues, no antifreeze valves, been running fine since 2022. Would happily use again. Caveat emptor, I have installed almost nothing but Stiebel Eltron since that job (only two others were Panasonic / Glycol) and S.E. designers say there's no need for Glycol in their systems.

It would, if we knew where due South was

Any reason that your plant room is huge?

He looks completely infectious... lol I'll belay watching that.

Who's the tiny man holding the big stick?

Indeed. My words are blunt, but honest. Good man.

No need for the olives, yet, as I hope the one you have on the pipe will be ok to save with the PTFE tape. You will need to test the repair and new valve for a few days, and then drain down a little to put 1x new inhibitor chemical in, but don't put that in until you know you do not have to drain down again, or that goes in the bin and you have to buy more. LINK This is a corrosion protection chemical which goes into the system and stays there for life.

When the pressure is zero on the boiler gauge, the system and radiators will still be nearly 100% full, if they are not on the next floor up above the boiler. You need to drain down the radiator you’re working on. Get one of these LINK and a radiator key LINK to open the vent at the top of the radiator. Until you open that, the water will stay in the radiator on vacuum. Drain out until there’s no more water to come out. Then fit the new valve. You need to get some PTFE tape LINK to go around the olive on the pipe (where you fear you’ve ’broken’ the pipe). You know when you’ve done this as the leak goes from bad to very bad. Applying this tape (10 turns) is to cover you from the olive having been crushed a little too much by over tightening with a spanner. Smear some jointing compound over the threads, over the olive (after tape) and this will mean you get a good seal without having to go Hulk on the spanner again. For the next tightening up, go easy, and try it first. Then go tighter just a 1/4 turn at a time if a small leak begins to show. The you close the vent at the top of the radiator. Then you go to the boiler and test fill the system back up to 1.5 bar on the gauge to check for leaks. If all good after 30 minutes, then bleed the radiator vent to get the air out. Then top the pressure back up (letting air out will make the pressure drop again on the boiler gauge) and run the radiators up to max temp for 30 mins and keep checking. If all good, select a nice shirt and get to the pub to celebrate. 🍾

Yes

When the cap is off, A is the key you use to turn valve B.

Yes, B will screw off with zero water coming out, as long as the valve D is at 90 degrees (flat) and not turned open in line with the silver can. Loosen it one turn at a time, and after 3 or 4 turns it will come away. The thread you have left will go to a Hozelock hosepipe fitting for a garden hose, if you want to drain to outside LINK (take the white 1/2" bit out and use the yellow 3/4" one

Ok. I asked because C shows signs of oxidisation of the brass (it's turned green) so that has leaked at some time too. Simple answer here is to just replace the valve with a new one. You can go for one with a DOC (drain off cock) LINK and this will be a straight swap. My guess here is that the chrome nut A wasn't made up with any pipe jointing compound LINK...or the olive behind that nut is squashed from overtightening. Have you used a spanner to try to tighten this up at all?

Get in there then....chop chop! If it were the cylinder leaking it would be a constant leak, not intermittent, and certainly it wouldn't have stopped when you stopped using the shower? What exactly is going on there?

OK. Unless I'm going colour blind, the cable coming up into the bottom of that junction box is grey? Next, it is defo not coming from the bathroom switch, as the cores in that cable are: Black, Brown and Grey + bare copper earth (green /yellow sleeve over it). So, the image you show isn't anything to do with the switch in the bathroom as the cable types are completely different? This would more likely go to the extractor fan with a timer in it? Keep looking

oops. Did you get an answer.....

Where is this valve leaking from exactly?

Everything at / above the point you want to open the system needs draining down.

Recessing is better than having a big step at the doorway

Yup. Some Agatha Christie shit going on there methinks.

That looks to have been taped and jointed vs skimmed?

@JamieB1917 You can thermally decouple the steel from a cold foundation / support by using any of many different, suitable products out there, capable of load bearing. Most recently I have used Bosig Phonotherm for this. Very robust, and very simple to cut / shape.

Just use the drain off on the magnetic filter, the silver can under the boiler. Easy!

Am I wrong in thinking that this switch is where the 230v supply for the MVHR is gleaned from? Or does the MVHR unit get its mains supply from elsewhere?