Nickfromwales

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?

Crikey. Is that switch a boost for the MVHR?! Expect the unit electronics to be nicely toasted if so…..unless it’s mains to a zero volt relay at the unit. The plot thickens. You can add a boost with a quinetic ‘momentrary’ wireless (RF) switch, with ease.

Most modern devices will cope at that temp. Try it first, fiddle after, only if absolutely necessary.

Supply N should be a neutral, currently it is shown as a brown cable eg a possible live conductor. This is very odd, but had been seen before e.g. where brown is a neutral but it should have been sleeved with blue sleeving to denote it is a neutral conductor. Conversely, the cable in load N is a blue cable which has been sleeved to suggest it is a live conductor! A proper mess in other words. Can you confirm which cable is the one going to the MVHR unit? The switch you show must be where the 3a fuse resides, which is replacing a generic 1G1W switch (see pic) usually used to turn a bathroom light on/off in a standard lighting circuit. What may be happening here is a local ring main has been taken to this switched fused spur (which is now your bathroom light switch), with a 3a fuse in it. Is that correct and the switch is not as I suspected eg isn't just a 20a switched isolator? A light circuit cannot be fed from a supply that offers more than 6a from a breaker in the fuse board, hence the need for the bathroom light feed to be capped by the 3a fuse. This should now be replaced with a 5a fuse. You need to identify the L & N coming into that switch first, the cable that goes on/off when you turn the circuit breaker on/off in the fuse board, that's the very first job. Which breaker turns this on/off, and what is it rated and labelled as, please? This cable needs to go directly to SUPPLY L & N of the fused spur. I assume it goes to the connector block instead, currently, but then you should be seeing a jumper cable, in blue, that goes from the connector block to the SUPPLY N terminal. This would be wrong anyways. I suspect the N for your bathroom light is picked up in that connector block, whereas it MUST be picked up from the LOAD N terminal ONLY. The cable from this location to the MVHR unit needs to be terminated into another switched fused spur, with a 3a fuse in it. This cable should go into the following: Brown (L) into the SUPPLY L terminal (so now two cables in that one terminal) and the Blue (N) into the SUPPLY N terminal. The cable which goes to the bathroom light, should be going into LOAD (1 x brown and 1 x blue per terminal), which gives the switched 5a feed to the light only. Basically, you need to disconnect everything here and start again. First question is, obvs, can you do this and do you feel competent to do so? If you're not 100% comfortable with doing this, with guidance, then DO NOT touch it any further, and get an electrician in for an hour to sort it. "Death is permanent", please try to avoid this

Unlimited hot water you said! Are you beginning to get cold feet? At least your head will be hot, with all that continuous hot water hitting it from the shower head 🚿 🥵

Liar. She has warned you 🤣

The only time he's ever been late for work was in a drinking competition in Oxford with my good self. They both came a close second lol.