Water tap lack of flow issue

[m_c]

The hot water tap on the sink in the bathroom flows well when first opened, but the flow then declines. Even if you close it and re-open it, the flow doesn't increase, unless you close it for a while.
Tap valve cartridge has been replaced, and did initially make an improvement, but a few days later, flow is down again.

The pipes to the tap are shared with the bath, and T-off somewhere under the floor, but the bath hot water tap runs fine.

The only other thing touched when replacing the tap valve, was the little isolating valve.
Can these go faulty and cause this kind of problem?

 

[Seadog]

Symptomatic of a blocked heat exchanger in a combi. Are all other hot taps OK?

 

[Tigman]

Are you on a combi boiler or gravity fed tank, or pressurised system ie megaflo

 

[JimmyS]

Might be a filter on the tap or crap at the back of an aerator restricting flow.

 

[123hotchef]

are there any mixer taps in the circuit?

 

[JimmyS]

Gate valve might fail but normally the valve would be a ballofix type which wouldn't normally fail to reduce flow.

 

[m_c]

Hot water is gravity fed, and no other valves except a ballcock after the hot water tank.

22mm (well probably old enough to be imperial) pipe from tank to bath, with the sink T'd of somewhere to 15mm pipe. Plus kitchen tap T'd of somewhere, which also runs perfectly fine.

 

[JimmyS]

Is it a modern monoblock type tap with small dia tails?

 

[mike os]

Airlock

 

[m_c]

Is it a modern monoblock type tap with small dia tails?

This kind of style -

but not that exact one.

I'm not sure what kind of fittings go on to the actual tap, as it's the classic bathroom wedged in the corner with minimal access setup.
I do know the copper pipes come up out the floor, there are isolating valves, then it changes to plastic upwards from there. I'll probably have to get a mirror to see how they then connect to the tap.

 

[awemawson]

Braided flexy hose feeding tap now kinked ?

 

[brightspark]

was the supply fast enough when it was 1st fitted .the original tap that is

 

[m_c]

was the supply fast enough when it was 1st fitted .the original tap that is

I wouldn't say the flow was ever great, but more than fast enough for washing your hands/filling the sink just using the hot water tap.
Now it reduces slow enough it takes noticeably longer to wash your hands if just using the hot tap. Probably a 5-6mm diameter column of water.

 

[gaz1]

The hot water tap on the sink in the bathroom flows well when first opened, but the flow then declines. Even if you close it and re-open it, the flow doesn't increase, unless you close it for a while.
Tap valve cartridge has been replaced, and did initially make an improvement, but a few days later, flow is down again.

The pipes to the tap are shared with the bath, and T-off somewhere under the floor, but the bath hot water tap runs fine.

from a quick read

does your bath tap run fine and also the kitchen sink run fine when the hot tap is turned on ?

so is it only the bathroom sink that has this issue?

 

[123hotchef]

dodgy check valve

 

[JimmyS]

Is there any debris at the back of the aerator on end of tap blocking flow when hot water runs as might not be noticable with high pressure cold?

 

[sparkysy]

I was going to say debris or such blocking the tap or isolator when the tap is turned on as it rises to a pinch point and blocks the flow. Only because you say it starts off fast and then slows!

 

[brightspark]

some of the inline isolators arent full bore flow so will well restrict on gravity

 

[JimmyS]

Right enough some ballofix valves are narrower bore and can get ones with a filter on them but wouldn't think they would have been used (filter balls that is)

 

[Justme]

If you have flexi's to the tap my money is on one getting twisted when you changed the tap.