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I have a very old central heating system that includes: 2 water tanks in attic - one for radiators and one that fills when I use hot water. I have a boiler and a copper hot water cylinder in kitchen. The problem I have is this...

Control panel is set to hot water only. This works fine

Control panel is set to water and heating, only hot water heats.

There is a little box next to the hot water cylinder with a sliding metal switch. The heating will only come on if I pull the metal switch to one side, but it keeps sliding itself back. I have to jam it in position but I'm worried that I maybe damaging it. It feels mechanical, and I think it's electrically powered as there is a wire coming out of it.

Is it easy to replace this box? What's it called?

moschops98 wrote:There is a little box next to the hot water cylinder with a sliding metal switch. The heating will only come on if I pull the metal switch to one side, but it keeps sliding itself back. I have to jam it in position but I'm worried that I maybe damaging it. It feels mechanical, and I think it's electrically powered as there is a wire coming out of it.

Is it easy to replace this box? What's it called?

Is this it?

http://www.awin1.com/awclick.php?mid=12 ... ised-Valve

Firstly, the manual lever can be locked in the open position. If you look closely, the slot the lever runs in has a small hook at the end which the lever can be set in to stop it returning to the closed position.

This "box" can be replaced. The electrical part can be simply removed without draining but of course the wiring would have to be carefully dealt with.

I ought to mention, replacing this part without testing could be a waste of money as there are other reasons the heating may not be working. Room stat or timeclock to name but two.

Thanks for the reply.

That's the fella! Even the brand name is correct. The configuration of the pipes though is not, but I'm sure they sell one.

I will check for the locking 'hook'. I've been using bits of wire, a screwdriver and now an old hand file without it's handle!

Why doesn't the lever on mine open by itself? It certainly used to, up until just before winter 2009 (the whole heating system is more than 20 years old)

Forgot to mention...
The room stat is in the same room as the boiler so I can hear it firing up.

Time lock - not sure what this is but I'm guessing the time control panel. All switches are set to the 'ON' position rendering any little pegs in the clock face redundant. I've tested this by turning the clock round and round, and when I do this there is no change coming from the boiler. Again, this is right next to the boiler so I can hear it.

moschops98 wrote:Why doesn't the lever on mine open by itself? It certainly used to, up until just before winter 2009 (the whole heating system is more than 20 years old)

'cause I guess something is broken!! The tricky thing is to identify exactly where the fault lies without spending vast sums randomly replacing parts.

Unfortunately, just because the timer and thermostat are making the right noises, does not mean they are working. You need to test each with an electrical tester.

The timer switching to on sends power to the thermostat. Providing the stat is calling for heat the power is fed to the valve motor which opens. As it opens, a micro switch is pushed closed feeding power to the boiler.

One thing I can say is if the valve proves to be faulty, you should only need to replace the top part (gears and motor). This is cheaper and avoids the draindown.