Radiators hot when Hot water only is selected

[Steven Campbell]

Our CH system is over 20 years old with a couple of tanks in the loft, boiler (potterton nettaheat 16-22) in the kitchen and some kind of pump under the kitchen floor.

I've noticed in the last few months that if I select hot water only, all the radiators but one heat up as if it is on the HW+CH setting.

I can't even turn off the radiators at the valves as the last one I did this to ended up leaking probably due to its age and its slight corrosion so I'd rather not touch them.

We need hot water but it is becoming unbearable with the heaters coming on in this weather.

I've googled and it looks likely to be a sticking valve but not sure if this is in the boiler or pump or somewhere else!

Can someone shed some light on the problem?

DIY wise, I've previously drained the system and replaced a couple of radiators so would this repair be in my scope?

Cheers

[Malcolm Stewart]

My system is similar in age and has a 3 port diverter valve (Honeywell) which is supposed to control the flow of hot water to

1 house and hot-water tank 2 house only 3 hot-water only.

It was giving trouble earlier this year after working fine for many years. Isolating the mains to the CH system and turning on again cured the problem. (Others here said I was imagining it, but I'm the expert as to what in my house, even if I don't know why!)

My valve is sited in the linen cupboard along with the pump etc. It's pretty obvious when you find it - it's got 3 ports, and wires coming away. See what happens when you manually select your various heating options. You should hear the motor turning the valve in some states, and not in others - spring return. Adding descaler or similar (Plumbers merchant, B&Q etc.) to your C/H header tank might cure matters.

[meow2222]

usually cause by a faulty diverter valve

NT

[adder1969]

One can usually manually place these in one position or the other using a lever on the side.

[Roger Mills]

Er . . not exactly. The lever allows you to manually move the valve from the HW-only position to the mid (HW+CH) position - useful when filling the system.

What it does *not* do is move the valve to the HW-only position if it is stuck somewhere else or if the spring return has failed. To do that, you would need to remove the actuator from the 'wet' part of the valve, and then rotate the spindle of the valve to the appropriate position.

We're assuming that the OP has a Y-Plan system, with a single 3-port valve. [If it's not like that - e.g. two 2-port valves, come back and tell us what you've got].

The first thing to try is to turn *all* power to the CH heating system off at the FCU (*not* at the programmer). That will sometimes reset a 'confused' valve.

If that doesn't work, the next thing to do is to remove the actuator from the valve (but leave it connected electrically). Check that the valve's spindle is not too stiff to turn, and put the heating system through its paces (by selecting each CH/HW combination in turn) and check what the actuator does in each case. It should then be pretty obvious whether the problem lies in the actuator (which is easy to replace) or in the valve - which is a plumbing job to replace but still easily d-i-y-able.

[adder1969]

Yes, I couldn't quite remember which way around it was but ingenious use of an elastic band or similar can fix the valve in either position provided of course that the internals of the valve are in good condition.

[Steven Campbell]

Thanks all for the suggestions. Once I get round to lifting the kitchen floor and have access to the CH bits under there, I'll post back for some advice.

Cheers

Steven.