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Radiators hot even though the central heating isn't on - any idea why?

(31 Posts)
Loueytb3 Sun 07-Oct-12 22:03:33

The past couple of days I've noticed that our radiators have been hot even though the heating has been off for a while. It seems to be while the hot water is on as they go cool after the hot water goes off. Anyone have any idea why and do we need to get a plumber out?

Oldandcobwebby Sun 07-Oct-12 22:09:31

My theory: Three way motorised valve not operating properly and allowing the primary feed to heat the domestic hot water and the radiator feeds at the same time.

Last time I bought one of these valves it was about £50ish. With any luck it is just the motor (known as the valve head). If so, it can be replaced in ten minutes without draining the system.

BTW, I am not a plumber! Hope this helps!!! smilesmilesmile

Marne Sun 07-Oct-12 22:12:11

Is it all the radiators or just upstairs? my upstairs (bathroom) ones get warm even when heating is off, also my cold water tap runs warm at times.

RightUpMyRue Sun 07-Oct-12 22:12:42

Years ago my mum had a new radiator fitted in the attic bedroom (old house, previously no radiator in the attic) and the plumber who fitted it( he wasn't a plumber, he was a musician who had done an evening course or something equally flimsy) said it was too much work to run the central heating pipes up to the attic, it would involve cutting into the walls to lay the pipes and re-plastering so he was going to attach the radiator the hot water pipes instead. It was on when the water was hot and cooled down when it was not.

Did a musician with an evening course in bodged plumbing fit your central heating system by any chance?

angel1976 Sun 07-Oct-12 22:13:50

We have the same 'issue', we had the boiler guy out when our boiler broke and he said it's fairly common for some people to 'link' certain radiators (usually the towel rails or radiators in the bathrooms) to the hot water system so that it warms/dries towels and heats up the bathrooms before you have a shower. Other than the radiators in our bathrooms, the radiator in the loft bedroom is also bizarrely linked to the hot water system but we suspect that's because that bedroom gets very hot in the summer and very cold in the winter! Those radiators should have individual thermostats so that they can be turned off during summer...

MrsMiniversCharlady Sun 07-Oct-12 22:14:14

Yes, we had the motorised valve replaced for this reason recently. Although it did involve draining down the central heating system and cost a lot more than £50. Wonder if I've been ripped off hmm

angel1976 Sun 07-Oct-12 22:14:57

RightUpMyRue Laziness makes a good reason too! grin

Way2Go Sun 07-Oct-12 22:18:29

oldandcobwebby is probably right. It's a common problem. You need one of these.
They have a manual override switch so you can use that until you get it fixed. They are cheap but buy a good brand.

Loueytb3 Sun 07-Oct-12 22:21:57

Its a new problem so I suspect not due to botched plumbing but to something going wrong, although time will tell I guess. The upstairs radiators are hotter but the ones downstairs are still warm. Glad it sounds like it could be easily fixed - can it wait a few weeks or is it something that we need to sort out asap?

We are waiting on a planning appeal which we should know about in 10 days time. If we win, we will be replacing the heating system anyway.

Way2Go Sun 07-Oct-12 22:23:33

If the plumber says he has to drain the whole system make sure he puts isolater valves either side of the diverter so that if it fails in future you wont have to drain the system.

You can't have enough isolation valves smile

I am not a plumber though so I might be talking shite.

Startailoforangeandgold Sun 07-Oct-12 22:37:14

Our bathroom radiator comes on with the hot water. Very handy for drying towels.
I'm told by he who knows everything (DH) that the system needs one radiator that can't be switched of to function correctly.

Pochemuchka Sun 07-Oct-12 22:45:57

Another one agreeing with oldandcobwebby.

Just had the valve replaced for the same reason. Heating off, hot water on = red hot house not controlled by thermostat.

Took the guy about 1 hour to do.

PigletJohn Mon 08-Oct-12 00:08:00

yes, it will be the three-port valve, and it happens when the cylinder is calling for heat, and the valve allows some of the heat from the boiler to go to the rads instead of to the cylinder.

If you had it done for £50, it was almost certainly just the motorised head that had failed (this is the squarish box on top) rather than the rubber ball in the brass valve worn out. The motor can be changed without draining down as it is detachable on all but the oldest models. You can also manually operate the lever on the side of the head, if the motor fails.

The entire 22mm valve and head costs about £80 depending on brand and supplier. Honeywell and Drayton are good and widely used.

There is a faint chance that it is caused by a wiring fault, especially if some inexpert person has recently fitted a new programmer or tinkered with the wiring.

If you have 28mm piping (not common) it will be more expensive.

Loueytb3 Mon 08-Oct-12 09:47:54

Thanks. Can it wait a week or two to be fixed?

PigletJohn Mon 08-Oct-12 09:58:57

It may cost you extra money since you will be heating the house more. Do you have thermostatic radiator valves? If not you can turn off the rads with the knobs on their valves.

Try altering the programmer timings so the HW only comes on twice a day, mornings and evenings.

Loueytb3 Mon 08-Oct-12 10:04:33

Yes we can turn the rads off so that would be a solution in the short term. Hot water only comes on twice a day but I think it is on longer at the weekend so that was when it was more noticeable. Its not so much of an issue during the week.

PigletJohn Mon 08-Oct-12 10:05:28

P.s. we are all assuming you have a hot water cylinder.

If you have a combi boiler instead it will be the diverter valve in the boiler.

Loueytb3 Mon 08-Oct-12 10:07:58

Yes we've got a cylinder smile

davegriff Mon 15-Jul-13 09:56:20


Similar problem. Hot water only selected, heats the rads. Thought that the problem would be the valve, so changes the motorized 3 way valve (correctly ie A to rads, B to water). Problem still there.

Anybody help, please?

jschwei Tue 06-Aug-13 12:16:34

I have the same problem. When I manually open the valves with the arm, there is pressure so they should be working.

One of the radiators even gets warm when hot water on and radiator thermstat is turned off (tested with heat on and hot water off--radiator stays cold, so valves are working and hot water is somehow getting into this radiator).

I had a plumber come round who told me the valves are working. He then gave me the typical, "your plumbing was put in wrong, and radiators are on how water circuit" (despite 10 years of being fine!).

Is it possible there motor on the valves are working but the ball inside is letting hot water through?

PigletJohn Tue 06-Aug-13 16:13:54

have a look and see if you can find a 3-port valve on the pipes. It will have heat-resistant flex attached to it. Observe that the 3 pipes go into it in a "T" shape. It will probably be close to your boiler and/or your pump and/or your hot water cylinder. It will most likely be branded Honeywell or ACL Drayton.

Turn the HW on and the CH off and see how many of the three pipes get hot.

If only one of your radiators gets hot, and it is the one on the bathroom, it was probably intended to work like that to warm toweks in summer.

fayjames Sun 25-Aug-13 21:27:15

We have been having this problem. We have now had a new motorised head fitted and a new thermostat, this seemed to solve the problem for a couple of weeks, but a couple of days ago it started again :-( We know we could just turn the radiators off but we have spent a lot of money on replacement parts and labour, so really this isn't the answer. Does anyone know what route we can go down now, it is really frustrating, Thanks

Ours was a valve which needed replacing.

The plumber said if that didn't work then he'd have to drain the whole system.

PigletJohn Sun 25-Aug-13 21:55:48

see above.

how many of the pipes get hot.

you had the head replaced but maybe the ball is worn.

Lynngarnham Wed 30-Aug-17 07:59:36

I live in a maisonette where the central heating is controlled by my neighbour, on Monday evening my bedroom was like an inferno even though my heater was turned off

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