Boiler heating radiators when we just put it on for hot water-why?

[amummyinwaiting]

Got home from hols in July and discovered that every time we put boiler on and turn knob to just hot water it also heats radiators. I know we should have dea;t with this earlier but didnt.
Is their anything we can do to sort it?
When it is just on it doesnt heat radiators.

My parents had this happen. Their plumber said it was a very common problem to do with mechanical (or something to that effect) valves. Apparently they could either get a new valve at great cost or just twiddle a knob when they want heating and again in the summer when they don't. Course it maybe something completely different, I'd just go with twiddling anything that doesn't look dangerous to twiddle and if it doesn't work call a friendly plumber.

You have a three way valve in your system (probably) that directs the hot water from the boiler into the radiators, the hot water system or both. This is probably jammed. If you know where it is you can take the motor off the top of the valve and turn it with a spanner as a temporary measure. Replacing it isn't difficult but it's time consuming as it involves draining down the heating. It's a DIY job for someone confident with plumbing.

this three-port valve (if you have one) is electrically operated depending on the sending from the cylinder thermostat (if you have one) and the room thermostat (you had better have one) and the boiler timer/programmer (you had better have one)

First please verify if you have these four things (they are all electrical and will all have cables going to them). You might not, depending on the age and design of your installation.

If and when you find the 3-port valve (it will usually be close to the boiler, and/or the pump, and/or the hot water cylinder, if you have one), feel the three pipes connecting to it and see if they are all equally hot. One of the pipes will be hot supply from the boiler, one will be the hot feed to the cylinder (if you have one) and one will be the hot feed to the radiators. these pipes will be arranged in a "T" shape with the valve at the centre. The valve is made of brass and will have a squareish metal cover over the electrical parts, with a cable goiung into it. The valve and its cover will be about six inches across and high.

BTW about how old is your boiler and the rest of the heating system? Do you have thermostatic radiator valves? Is it just the upstairs rads that get hot, or all of them?

p.s. the valve might be jammed, but it is more likely just worn. Or maybe there is an electrical problem. When we know more it will be easier to say what needs doing.

What do you mean when you say "When it is just on it doesnt heat radiators" and what names and numbers are on the control you are talking about?

We had the same problem with our boiler a while back. Boiler engineer replaced the diverter valve and it's been fine since.

thanks everyone-only just got in from wrk so will post tommorow with answers for questions.
Eaglebird-did it cost much?

I think we might have the same problem . We only moved in in April - boiler was checked over but sounds like we should get the plumber back...

Mummyinwaiting, we have a breakdown cover policy for the boiler, so it didn't cost us anything (apart from the monthly premiums of course).

Are you a British Gas customer? I'm not, but I think they do reduced rate boiler repairs for existing customers. I heard an advert on the radio a while back.

Or try asking around friends & neighbours for recommendations for a boiler engineer. Better than picking one out of the Yellow Pages with a pin. Plus, if you ring up and say 'I've got a problem with my boiler, and I suspect it's a faulty valve', the engineer might think you're a boiler genius and be less inclined to rip you off :)