Intermittent hot water - please help

[Nicola76]

We have a power shower and there is an ongoing problem that our local plumbers have been unable to solve so I was hoping someone here would be able to provide an answer.

Every so often when using the shower it starts up fine and then stops after about 30 seconds when the water turns cold. Then the temperature on the shower has to be lowered until the shower starts up again and then the temperature can be raised again. Then it usually stops, again after a few seconds, as the water turns cold.

When I try the other taps in the bathroom they also run hot and cold. Eventually something seems to kick in and the shower stays hot.

When the shower is turned off then occasionally there is a loud noise from the hot water tank in the loft and lots of banging of the pipes. This carries on for about five minutes. I have noticed, though, that when this happens the shower works fine for a few weeks but if the pipes haven't rattled for a while then the shower starts to play up.

Is this an airlock? We often have problems with the upstairs radiators and have to bleed them every week - would this cause problems with the system?

Sorry for the long post but the problem is very annoying and I hope someone might be able to help me.
Thanks

 

[breezer]

I am not a plumber or heating engineer.

first i must ask has it always done this or only just recently? if so has anything been added or changed?

From what you say

When I try the other taps in the bathroom they also run hot and cold. Eventually something seems to kick in and the shower stays hot.

When the shower is turned off then occasionally there is a loud noise from the hot water tank in the loft and lots of banging of the pipes. This carries on for about five minutes. I have noticed, though, that when this happens the shower works fine for a few weeks but if the pipes haven't rattled for a while then the shower starts to play up.

Is this an airlock? We often have problems with the upstairs radiators and have to bleed them every week - would this cause problems with the system?

you have to know that hot water only comes out of the hot tap because cold water goes into the bottom of your hot water cylinder from the tank in your loft (it is this pressure that forces out the hot water)

and as you also say that you "get noises from your loft tank"
i am wondreing what happens if you push the ball cock in the tank down, does water flow strait away? it may be that it is sticking and so not letting water into the tank, which then goes into the cylinder (airing cupboard) to force hot water out, also this would cause air to be drawn into your central heating system, which is why the radiators need bleeding so often.

If this is the case you only need to change the washer on the ball valve inlet, or change the whole ball valve assembly.

or i could be totallly wrong. but do try pushing the ball valve down in your loft tank first ( It must work first time every time) at least you will either find the answer or you can rule out the ball valve.

 

[Nicola76]

Thanks for the reply. I shall try the ball cock and I'll see what happens.
The problem started when we got the shower installed - it is a stand alone one - a few years ago.

Thanks for your help.

 

[breezer]

I am not a plumber or heating engineer.

as i see it you are saying that you have had this problem since the shower was installed?

If the ball cock is working ok then it must be that the shower installation is wrong.
A power shower must get equal amounts of hot and cold water at the same time. to do this the hot water must come directly from the hotwater cylinder (they install a special "joint" the name escapes me just now) and the cold directly from the tank in the loft.

The shower pump has two impellars so that it pumps both at the same speed. Unfortunately the cold water from the tank is also supplying both the cold water for the shower and the cold water to push the hot water out from the hot water cylinder.

If the ball valve is sticking then it will not fill the tank up fast enough, so it empties the tank and sucks in air.

there are two solutions.

get a bigger tank in the loft (but it will need more support, so it may not be practical)

see if the pump has a speed control and slow it down (not sure i do not have one and i doubt it has)

the other thing you could try is to turn the shower on and go into the loft and see what happens, that way you will know for sure.

I hope it is the ball valve sticking.

I once wanted a power shower and i couln't have one because the loft tank was too small and a bigger one could not be installed because there was no room for it. I was then told how a power shower works which is how i know.

To resolve my problem I moved house (very extreme) and 2nd thing on the agenda was to have a combi boiler put in which uses mains water pressure for the shower.

Perhaps if your existing boiler is old you could consider a combi boiler?

 

[ogoshi]

The ballcock sounds very feesable,but also check that the hot supply to the shower is the first joint in the pipe after the pipe leaves the top of the hot water cylinder,but it must not come from the rising section of pipe that comes out of the cylinder.(it must come from the horizontal pipe or where the pipe drops after the horizontal)The rising pipe is the vent which carries the expansion water and air to the storage tank in the loft.