Downstairs heating constantly on

Krazyhelpless · 2026-01-09T18:59:39+0000

We have a heating issue where the boiler is staying on and heating downstairs. It's a 3 zone system, upstairs, downstairs and hot water. The upstairs and water are functioning as normal, only coming on when set to on at timer. Downstairs remains on with timer turned to off its a horstmann 3zone timer.

The only way I can stop the boiler is being unplugging it in the outside boiler house or tripping the heating switch at mains to turn downstairs heating off. I'm guessing it's an issue with the downstairs valve? Upstairs the hotpress contain the valve heads for upstairs and hot water. I've no idea where to find the downstairs one. Can anyone help me trouble shoot or know the typical locations for downstairs valves? I'm based in NI. We're on oil fired heating with a popular 90 boiler located in a boiler house at end of the garden

CountryFan · 2026-01-09T19:48:07+0000

Yes, it sounds like a stuck microswitch. Is it definitely not in with the others?

Krazyhelpless · 2026-01-09T20:09:08+0000

CountryFan said:
Yes, it sounds like a stuck microswitch. Is it definitely not in with the others?

Yeah I've searched everywhere in there, assumed it would have been there too.

CountryFan · 2026-01-09T20:16:12+0000

Krazyhelpless said:
Yeah I've searched everywhere in there, assumed it would have been there too.

Well it has to be somewhere. Maybe it’s downstairs or even with the boiler?

Krazyhelpless · 2026-01-09T20:28:46+0000

CountryFan said:
Well it has to be somewhere. Maybe it’s downstairs or even with the boiler?

Tried the boiler too and have been looking around the house to no avail. The wiring box with the other two only has two orange wires so it's not being wired here. Wiring box

CountryFan · 2026-01-09T20:53:47+0000

Krazyhelpless said:
Tried the boiler too and have been looking around the house to no avail. The wiring box with the other two only has two orange wires so it's not being wired here. Wiring box

Nope, not in there. Is the hot water a mid position valve?

Harry Bloomfield · 2026-01-09T21:05:02+0000

Krazyhelpless said:
Tried the boiler too and have been looking around the house to no avail. The wiring box with the other two only has two orange wires so it's not being wired here. Wiring box

You only appear to have the two orange wires, plus a brown, with grey outer, feeding the boiler. Disconnect all three, and test which one is live, then follow that back, to the valve actuator.

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Downstairs heating constantly on

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