Hot water pressure All aspects of plumbing questions and answers, help, tips and information

[trevors50uk]

When I turn the hot water tap on the kitchen sink mixer taps the hot water comes out and heats up, but after a while the pressure drops and the water becomes a trickle. It is fed through a combi boiler.
Is this a tap problem or is it the boiler? would appreciate some guidance. Trevor

[plastic_man77]

@ trevors50uk

Sounds like a tap problem.

Do you get the same behaviour at other hot outlets? If not, then it's sure to be the mixer. The tap probably slows to a trickle as the washer in the tap expands due to the heat and blocks the port- can you open the tap any more to increase flow?

[trevors50uk]

Other hot water taps working fine. Opening the tap fully doesn't increase the flow.
This problem tap is at the end of the line from the boiler, that's why I wondered if the boiler was the problem. Do you suggest changing the mixer tap? Thanks, Trevor

[plastic_man77]

@ trevors50uk

If the water pressure and flow is ok to start with from the mixer, but a flow problem develops only as the water temperature increases, then change the mixer. There isn't any kind of blockage in the pipework, otherwise it would present itself as soon as you open the tap and there's not a problem with the boiler if the water temperature and flow is ok at other hot outlets.

Something you could try- turn the boiler off so that the water doesn't heat up and run the mixer tap. If the tap continues to run fine while the water is cold, it's definately the mixer at fault.

[trevors50uk]

Many many thanks for that. Will try.

[Dick Puller]

@ trevors50uk

If the water pressure and flow is ok to start with from the mixer, but a flow problem develops only as the water temperature increases, then change the mixer. There isn't any kind of blockage in the pipework, otherwise it would present itself as soon as you open the tap and there's not a problem with the boiler if the water temperature and flow is ok at other hot outlets.

Something you could try- turn the boiler off so that the water doesn't heat up and run the mixer tap. If the tap continues to run fine while the water is cold, it's definately the mixer at fault.

Sorry, but that's not the case. If you have a blockage in the supply pipe, the pressure & flow will be high, but that will diminish as the water is restricted by the blockage. So you could well have a part blocked pipe.