DIY Doctor UK DIY Forums

For the last few months, I have had reduced/non-existent flow of hot water out of my taps: kitchen, bath and basin.
Water is hot when it [i]does[/i] come out, but often there's
- no water coming out...
- or there is a pathetic dribble...
- or there is a long lag (2 mins-20mins).

I live in a 6th floor flat in London, so I expect problems with water pressure every now and again (Thames Water leaks, high demand, etc.) but this is happening regularly - both at high demand times and low demand times (e.g. 3am) and I have additional pumps (in my flat) for the CH and HW.

Thames Water say pressure to building is average 2.2-2.4 bar.
Pressure valve gauge under kitchen sink is at over 1 bar (and has remained stable for last 2 years) but this does not accurately reflect the pressure coming out of the HW tap.

On opening hot water tap, if there is HW, I can hear the pump working, but not a peep when there is no water flowing.

Potterton Prima 40F boiler 'seems' OK as CH working fine.

I am tempted to treat it as an air-lock and follow the [url=https://www.diydoctor.org.uk/projects/curingairlock.htm]article[/url] but worried that if it's limescale build-up this will cause a problem.

The flat is 50 years old and looks ancient. Could it be that it's on its last legs or something more sinister?

Any ideas? Thanks in advance!

Like I said in my last post, If your cold water pressure is ok - then it's nothing to do with Thames Water.

Is there a tank or cylinder in your flat ?

When the hot tap does run - can you hear a tank filling ?
It's probably that the ball valve needs on overhaul/replacing. When you run a bath the tank may empty quicker than it is filling, that could be why your hot tap stops running.

I am absolving Thames Water from this one. I just checked with them re: current pressure as have been without water in the past due to big leaks in the area.

There is a tank and an immersion heater in a cupboard, which I can hear filling up on the odd ocassion that someone has a bath. It's true that it is necessary to sometimes run it in two stages because the tank is slow to re-fill, but this is not the problem that we are experiencing currently.

Basically, there is intermittent hot water (at random times, it appears) despite no prior usage from within my flat. Sometimes, I am unable to have a shower [mixer shower tap] in the morning even though I am the first to use the hot water. There is a hot trickle (if I'm lucky) or none at all. The same applies to the other taps.
A few hours later, I'll try again... and nothing. 10 minutes later, it's fine.
Try again after another 10 mins and a trickle...

My washing machine has cold and hot inlet hoses so no doubt this will also be affecting my laundry..

I flushed the hot water pipes with cold water from mains (in case of an air-lock) but this has not helped.

Do you still think I need the ball valve in the tank to be replaced or could it be something else?

P.S Thanks for all your help, htg engineer!! :wink:

When you get no hot water, check the level of water in the header tank over your cylinder. If it's empty you know that is where the problem lies.

If the header tank is full, you almost certainly have a physical blockage in the pipework (often insulation debris). Remember, the blockage could be on either the hot water distribution pipework (are all hot taps affected at the same time) or on the cold feed pipe to the cylinder.

I have had for some time an airlock within my hot water system?

When i turn the hot tap on it flows normal has a few spurts then slows down almost to a stop, then it will repeat this cycle?

Jezclayton, Thanks for your help!

Update: I have had a plumber take a look and for now, he's replaced the seal on the ball valve on the hot water tank (all gunked up) and says the problem is with the 'floor switch' on the pump.

When the pump kicks in (intermittently) the hot water comes out of all taps, but there is a delay in switching itself off after taps have been closed and sometimes needs to be switched off manually at the socket.
When HW taps are opened and the pump doesn't switch on, there is no water but the following (temporary) fix appears to work: knock the pipework directly connected to the pump and, hey presto!

He says the floor switch can be replaced but not much more to replace the whole booster pump. Been quoted about £400 to have one installed
(Monsoon, 2 Bar, Single).

Should I get him to make sure that there isn't a blockage on the hot water distribution pipework (all hot taps are affected at the same time) or does his diagnosis sound about right?

Cheers!

Can anyone out there please advise.
This morning I woke to no hot water.
I have tried the hose method, putting on the hot tap first and then turning on the cold, hot water runs for about a minute and then stops.
Thanks in advance

Update to original thread:
Plumber fitted new 2 Bar pump (to replace original 1.2 Bar pump.
Hot water flows like never before - "a tamed tsunami".

Problem Resolved!