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Plumbing

Half of the new radiators hot when only hot water is on

Jing Wu 10/09/2026 - 9.30 AM

Hi there, I have got an unvented water tank in my new house and had all the radiators replaced for before I moved in. It was tested by the installers by turning the heating on and all the radiators worked fine. But after I moved in, I just found out that while only hot water is on, some of the radiators are on too. Anyone knows what may cause that? I ordered the radiators from an online shop and when they were delivered there stickers with 'inlet' 'outlet' on the radiators which the installer didn't always follow. I was told by the supplier that the installer needed to change something inside of the radiator to change the inlet side to outlet. But the installer said that was okay. Will it be the possible reason for that? Many many thanks

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3 Answers

Marius Baciu

No reviews yet

Hounslow
2 port valve
Answered11 September 2026
1

Ignite plumbing

Rating: 5 out of 5
Norwich
This sounds like a stuck 2 port motorised valve, basically when the boiler is calling for heat, the heat is going around the hot water coil and the heating system. Have a look in the cupboard and listen for a buzzing sound, or could be in manual override. Cheers steve
Answered11 September 2026
1

Matheson Heating

Rating: 5 out of 5
Canterbury
Yes most likely an issue with the 2 port valve not closing on the heating circuit.
Answered11 September 2026
1