Another central heating problem :)

-BA- · 16 Jun 2009 at 22:42

We have a fairly old CH system and although it is controlled by a unit downstairs, there are individual thermostat valves on each radiator. Until now these have been pretty good but for some reason one of these valves now seems to be stuck on max and although the central heating is currently off, hot water is bleeding through to this radiator and it is on full blast.

Do we just need to get this one radiator flushed through or the whole system? Does this even seem like the likely cause (ie: a blockage in the valve)? There are 9 radiators on the system so a ball park figure of cost would be great if anyone can help.

Thanks

Werewolf · 16 Jun 2009 at 22:50

if it's a thermostatic valve they do have an annoying tendancy to lock open or closed.

You've got two choices, if it's stuck open:
1: replace it whilst the weather is nice - probably the best bet.
2: Try and force it closed.
Normally they are two part, the thermostatic lump which screws on top of the actual valve and works (normally) by teh wax expanding and pushing the "pin" on the top of the metal valve body down (closing it), and the metal valve body.
If it's stuck you can often take the thermostat part off and push the valve pin (or pull it carefully if it's stuck closed), repeat a few times to make sure it's moving ok, that will sometimes free it up enough for it to continue working but it's not a long term solution

It's the sort of job that for a replacement valve you're looking at about £5-20 for parts depending on what sort of valve it is and the style (straight/right angle, plain/chrome etc), and depending on the plumber it could well be minimum call out (if he's got the gear to freeze the pipes to avoid the need to drain the system, otherwise add time to drian/refil the system).

Flushing the system would probably help prevent it happening to other valves, but if the valves already sticking a flush on it's own probably won't do much.

dannyjo22 · 16 Jun 2009 at 22:50

Surely if hot water is getting to the rad and the central heating is turned off then the problem is with the valve in the airing cupboard?

Doesn't sound like it needs flushing at all.

-BA- · 16 Jun 2009 at 23:08

This specific problem has only occured recently where this vavle is stuck open but there has always been a problem where the first 2-3 radiators have allowed hot water through if I opened their individual valves. So yes I guess there could be an additional problem in the airing cupboard at the immersion tank.

Werewolf · 16 Jun 2009 at 23:12

hmm hadn't thought of that, although it depends to a degree on the setup - a couple of our radiators are fed prior to the main valve (bathroom being the main one), and rely more heavily on their individual thermostatic valves than the rest.

It could be the heating/hot water (3 port valve) is playing up as well.

St0rmer66 · 17 Jun 2009 at 00:05

Almost certainly NOT the thermostatic valves. They generally get stuck closed quite often but very rarely stuck open.

It's probably the 3 port valve as Werewolf says. They have a habit of getting gunked up and then not closing properly for either the hot water or heating. This means (in your case) that even when you just want to be heating the hot water, some of the heat is getting through into the heating circuit. It's probably only slightly stuck open, hence why only one radiator is getting hot and not all of them.