Plumbing mystery overflow from loft

[Cubist]

Thanks for these latest photos and the words from your plumber and yes, what he says does make sense. What he is confirming is that as the water in the cylinder gets hot it is expanding to fill the expansion pipe and this is then spilling back into the tank to overfill it beyond the level of the overflow pipe. By increasing the height of the pipe coming up through the floor from the hot water cylinder MAY prevent this in the future PROVIDED the water temperature in the cylinder does not rise significantly above current levels. This also confirms why, when the apprentice reduced the flow rate from the boiler, the water flow through the overflow significantly reduced and temporarily halted.

In my personal opinion the pipework in your loft is what my father would have described as a 'buggers muddle'. It is needlessly complex and poorly designed. Also, and echoing @malcolm and @fernicarry s comments above, that main cold water tank is very poorly supported and the routing of the expansion pipe/filler pipes from the hot water cylinder are less than ideal - may be the apprentice did that work too but he/she at least had one good idea. This entire arrangement needs to be re-visited by someone who knows what they are doing and constructed to SAFELY carry the weight of the water load and handle the heat from the new boiler system.

 

[Kathy]

Thanks Cubitt. Plumber - said he would come round later. He does know his stuff. Just super busy this time of year.
Will discuss improving the Heath Robinson design with him.

 

[Cubist]

Thanks Cubitt. Plumber - said he would come round later. He does know his stuff. Just super busy this time of year.
Will discuss improving the Heath Robinson design with him.

Never thought I would say this but... HR would have produced a better design.

 

[stuart45]

If there was a hole in the coil I'd have thought the pressure would be high enough in the cylinder because of the extra height of the tank, so the clear water would be going into the heating system, rather than the dirty water coming out of the taps. Only a theory, as plumbing isn't my trade.

 

[a twig]

Another of my dumb questions, for @a twig and/or @Kathy - What colour would the hot water be if you turned on a basin, sink, bath or shower tap/faucet AND there was a leak in the cisterns heating coil?
If the water is crystal clear then there is no leak in the heating coil.
If the water is black or even slightly grey then there is a leak in the heating coil.

Leak from coil would go the other way as HW tank is a higher pressure, so taps will still be clear - and overflow from CH tank would gradually become clear as the oily inhibitor water gets flushed out over time.

 

[a twig]

The tank set up annd unsupported pipe work isn’t great but I’ve seen worse to be honest.

The header tank looks pretty full - your new boiler is likely actually hitting the target temperature for the CH system (or set to a higher one vs the old one) which would mean greater expansion and thus possible explanation for the issue since the new boiler and might give hope that the coil in the hot water tank isn’t leaking.

Tying up the header ballcock so it doesn’t refill the tank could still be a valid test to do to narrow down causes, if tying it up for a couple of days stops the overflows then replacing the ballcock valve with one that fits the tank and adjusting it to stop filling at a lower level would solve your issues, although while a plumber is up there then worth tidying up and supporting everything properly.