Head scratching so much, i'm getting a bald spot (3 port valve issue)

[Mighty_G]

So...
My mother moved into her new home a few months ago , house about 20 years old. The central heating is open vented.

Her heating had an issue where the rads would come on when only calling for hot water.

So Friday I changed her 3 port valve, with an identical valve, found the old valve full up of rubbish.

Once the valve was in I went to untie the ball valve. It was at this point something odd happened. When I went to drain the rads they wouldn’t all drain, it felts like there was very little water pressure in them if any. And now thinking back I'm almost certain when i untied the ball valve there was still water in the tank.

So I was thinking air lock / blockage issue and turned the boiler on to call for hw and ch. when doing that (and still) the boiler runs for about 20 seconds and then cuts out.

There’s a bleed valve in the airing cupboard above the valve and pump and when I open that no air or water comes out, I took that valve off this morning and found no water, tried blowing through that and can hear water bubbling - somwhere. I replaced that valve any way with an automatic one.

This morning i connected a hose to a lower drain off point, ran that, and filled all the rads (with real pressure coming out of them this time), and bled the automatic valve (I had closed it manually), only a small amount of air seemed to come from there. Not sure if it matters but when filling with the hose it did produce water from the overflow - but i think that's expected. What i'm not sure of was if any water was going back up the supply pipe from the feed task

Does anyone have any ideas of what could be the issue ? Plumbers are so hard to get hold of around here and now she’s without hw or heating so really want to get this sorted for her.

One thing that happened before the is install was I checked the electrics which were fine, but whilst doing that I made a slight f-up by shorting port 5 and blowing the fuse in the heating fused spur, I replaced that though and checked all electrics again so assume that’s not related.

 

[Chuck]

Airlocks are possibility. As you seem to know, these are less likely if you fill the system upwards from the lowest drain point than downwards from the expansion tank.

If the old valve was 'full up of rubbish', however, then there may well be sludge blocking pipework elsewhere in the system. A likely place for this to build up will be around the bottom of the riser connecting to the expansion tank. Draining such a system can move sludge around and create blockages (full or partial) in the processes.

Sludge usually contains enough magnetite to be detectable with a strong hand-held magnet; this will be attracted to regions where there is a lot of sludge.

There are lots of threads on this forum giving how-tos and discussing the pros and cons of power-flushes vs drain-and-refill cleaning. Use the search box at the top right of this page.

Assuming the boiler is suitable (or is being replaced), I think that thorough power-flushing, conversion to a sealed system and the correct dose of good-quality inhibitor is the best value for money over the medium / long term.

Some favour 'semi-sealing' the system. In my opinion, this is okay as long as the home owner is technically minded enough to keep an eye on it but this is the exception rather than the rule. One must also keep in mind that heating systems last quite long periods and someone who is happy to nip up into the roof every few months when they are 60 may not be so agile ten or twenty years later.

 

[Mighty_G]

Sludge usually contains enough magnetite to be detectable with a strong hand-held magnet

Assuming the boiler is suitable (or is being replaced), I think that thorough power-flushing, conversion to a sealed system and the correct dose of good-quality inhibitor is the best value for money over the medium / long term

Thanks very much for the response, I think pressurising it will be the eventual outcome as she wants a decent shower too and has talked about a shower pump.

For now though to get her up and running I’m going to try the magnet option as see if I can find anything, I’ll also search the forum for cleaning techniques as looks like that’s my only short term solution