Hot tap in bathroom intermittent failure to flow

[Clowance]

Hi, this is my first post so please be kind! Have had a problem with the hot tap on bathroom sink for months now, sometimes its fine, sometimes no water comes out until fully turned on, sometimes you turn it fully on and nothing comes out until you start turning it off again. Husband (an electrician so not complete amateur) has changed the tap, it has a new isolating valve on the pipes. Could it be an airlock or something else?
Advice please!

 

[Riley]

Pic of the tap???

 

[Clowance]

 

[steadyon]

Good chance its an airlock. If you have a wet and dry vacuum cleaner, the next time it happens suction out the hot tap. If the water starts flowing that's most likely the problem.

Cure is a bit more difficult, as its most likely a pipe run going up hill then down again rather than a constant descent to the tap (as far as practicable).

 

[Chuck]

What's the history, exactly? Did the tap work fine for years and then this started happening for no obvious reason? Or, for example, was there some work done somewhere and this started happening soon after?

Do you have a traditional low-pressure, so-called vented, hot water system with a tank in the roof and a cylinder? Or something more recent such as a combi boiler?

 

[Clowance]

What's the history, exactly? Did the tap work fine for years and then this started happening for no obvious reason? Or, for example, was there some work done somewhere and this started happening soon after?

Do you have a traditional low-pressure, so-called vented, hot water system with a tank in the roof and a cylinder? Or something more recent such as a combi boiler?

The tap did used to work, but I cant remember when it began, I do know we changed the tap and the isolation valve because we thought it might help. We do have an ancient central heating system, put in in 1991 with a cast iron potterton, an immersion heater in a hot water cylinder and tanks in the loft for storage of radiator water and hot water feed. The cold water all through house runs off the mains.
thanks for your help so far, I will try the vacuum cleaner idea above but any more ideas gratefully received. I tried to block the mixer tap in the kitche (idea off youtube) but merely succeeded in giving myself a cold shower!

 

[JCplumb]

If you don't have a wet vac, use a piece of hose to join the tap outlets and blast a few seconds of cold water up the hot supply. Should clear any air lock.
You'll get wet though.

 

[JCplumb]

If there's an aerator on the kitchen tap you might have to remove it before you can do that, but if the kitchen tap has decent flow it might not shift the air lock that is affecting the bathroom tap.

 

[Chuck]

The tap did used to work

In that case, I'd say an airlock is the likely suspect followed by a foreign body in the pipe, probably stuck at a point where the diameter reduces. So try the method @JCplumb suggested in post 7.

If not, we've established that it stopped working of its own accord and your husband replaced the tap with a new one, which made no difference. Does the tap on the bath work okay? Can we assume that there are no pumps, stop-cocks, gate-valves, etc. to confuse matters?

 

[Welder]

I'm not a betting man, but my 10p is on rubbish from the tank getting caught in the cheap (restricted) iso valves.

Cure. Remove the iso valve completely. Temp mount a pipe and hose so it dumps into the bath. Open the supply full bore and let it run for 60 seconds. Keep the plug in the bath and see what pops out. I've captured all sorts this way.

What happens is that the rubbish is pushed up to the iso valve and then restricts flow cosy it can't get through. As soon as you turn off the flow, gravity causes it to drop back so when you look at the iso it all appreas clear.

Have fun.

 

[Clowance]

Thanks for all the replies, we will try everything and likely something will work! Have a good evening everyone.