Hot water on -> radiadors are hot HELP!

[JoeJoe]

First apologies - I am sure I have seen a similar question in the past, but couldn't find it for some reason...

Problem as per subject:

Recently, despite having the heating off, some (not all) of the radiators in my house are hot when the hot water is switched on.

As you probably guessed by now, I am no expert on the subject, but I believe the system is a conventional one, based around an ageing ServoWorm Elite 80 boiler (to be replaced next year when the extension is to be built). One possible clue it that we had to have a pump replaced in it last year when we bought the house when we realised that the only way to get hot water was to turn the heating on... Also, both heating and hot water seem to work OK apart from the hot radiators getting warm.

Any idea what is going on?

Thanks in advance.

[dale hammond]

[Lobster]

I'm sure you have - this comes up quite often ;-)

So it used to be OK (ie you could heat heating and hot water independently), right? Just that if not, it's possible you have a really cheapskate system which was not intended for them to work independently, ie in summer you just turn all the rads off manually or turn the roomstat down really low to force 'always off'.

More likely - assuming you did used to be able to isolate the CH - is that you have a failed 3-way motorised valve, something like this:

if you can find one - probably near the HW tank if you have one? They normally have a small sliding lever which you can actuate manually to over-ride the built-in motor, so if the motor has failed you should be able to tell by mimicking its action this way. Have a look at the FAQ, which explains all about how these work IIRC.

If the motor has failed, you should be able to replace just the motor on its own without removing the whole valve and draining the CH system, which is a much bigger job.

David

[Set Square]

It *could* be a problem with the mid-position valve (if you have one) but it's unlikely to be a failed motor. The motor moves the valve *from* the HW position to the 'mid' and CH positions - and a spring returns it when the motor is turned off. If the motor fails, the valve stays in the HW position and you *don't* get warm radiators. If it *is* the valve, it's more likely that the mechanical part of the valve is stuck or that the spring return isn't working.