Stop gas boiler heating the water tank

Páid · 03-01-2026 03:48PM #1

We have a gas combi boiler in the kitchen. When it’s on it heats the water in the water tank which gives us hot water in the taps.

We rarely use the hot water in the taps. Is it sufficient to close the red valve so that the gas boiler only heats the radiators?

Lenar3556 · 03-01-2026 04:01PM

Yes, or closing the top thermostatic valve should be sufficient and easy to reverse in the future.

It’s unlikely you have a combi boiler, probably conventional. Combi boilers heat domestic hot (tap) water directly, typically without the use of a cylinder at all.

Cyclingtourist · 03-01-2026 04:06PM

https://www.boards.ie/discussion/2058430626/stop-gas-boiler-heating-the-water-tank

If yours is the same as mine the valve shuts off the heat to the radiators but in the normal position heats both radiators and tank. So the answer, at least for mine, is no it never shuts off the heat going to the tank from the boiler.

Páid · 03-01-2026 04:06PM

it’s a Greenstar condensing boiler.

Páid · 03-01-2026 04:11PM

Yes, or closing the top thermostatic valve should be sufficient and easy to reverse in the future.

In order to close that fully don’t I need to take the top off and use a pliers?

It’s easier just to close the bottom one.

Thanks for your help.

Lenar3556 · 03-01-2026 04:44PM

https://www.boards.ie/discussion/comment/124113714#Comment_124113714

No, there is nothing to turn with a pliers. Just turn the thermostatic head to 0. If it’s faulty and not working, it’s fine to close the red balancing valve on the lower pipe. If you decide to reopen in the future, about 1.5 turns would be the correct amount, opening fully will likely unbalance the system.

Lenar3556 · 03-01-2026 04:44PM

Can be combi or conventional.
Most likely conventional given you have a cylinder.

Lenar3556 · 03-01-2026 04:46PM

https://www.boards.ie/discussion/comment/124113697#Comment_124113697

Not in this case. The valve is on the cylinder coil and will isolate only the cylinder boiler flow to the cylinder, which will stop it heating.

Páid · 03-01-2026 04:58PM

No, there is nothing to turn with a pliers. Just turn the thermostatic head to 0. If it’s faulty and not working, it’s fine to close the red balancing valve on the lower pipe. If you decide to reopen in the future, about 1.5 turns would be the correct amount, opening fully will likely unbalance the system.

Thanks. I’ve turned off the TRV and left the lower one at 1.5 turns open.

Stop gas boiler heating the water tank

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