DIY Doctor UK DIY Forums

When I turn my shower up to full the boiler shuts off (and so the shower runs almost cold). When I turn the shower dial back down, the boiler kicks in again (but the shower isn't running warm enough to use).

This started happening straight after a boiler service. The engineer says he thinks it is the shower that is faulty. However, I want to be sure before buying an expensive new part for the shower.

The thing that is worrying me is the same thing happens when I test the taps in the wash basin. If I turn the cold tap up to a high flow when the hot tap is running, the boiler shuts off and doesn't heat the water to the hot tap.

Just for some background info: I have also just had the diverter valve replaced as the hot water stopped working altogether while the central heating was still working. This happened after the shower problem started and a new diverter solved the problem with the hot water (but not the shower)

I hope this all makes sense to someone!?

MrsAddams

"This started happening straight after a boiler service. The engineer says he thinks it is the shower that is faulty."

Oh really! Not very logical and sounds like a smokescreen.


"However, I want to be sure before buying an expensive new part for the shower.

The fact that this only started to happen immediately after the boiler service kinda implicates the engineer who did the service and unless you have a one in a million coincidence it points to the boiler NOT the shower.


"The thing that is worrying me is the same thing happens when I test the taps in the wash basin."

So it is the boiler then. Get the engineer's company (preferably at a supervisory level) back in, tell them you are not satisfied and want it fixed!

Cheers

Does the boiler shut off ? or is it just not heating the water ?

With a tap open fully it may be going through the boiler too quick to heat the water, possibly because the gas pressures are incorrect.

Unless the service engineer has changed the gas pressures, it's going to be hard to prove he was to blame - and the most of the time it isn't the engineer to blame - just coincidence.


htg

The boiler actually shuts off. You hear it go quiet just as if you're not asking for hot water anymore.

It's as if turning the flow/pressure of the water up for the shower (or cold water tap) is asking too much of the boiler and causing it to trip off.

I'm not looking to blame the engineer. I only want to be able to fix it and don't want to go to the expense of getting a new part for the shower (£100 plus) on top of the £200 plus it cost me for the diverter pump fitting, if that isn't what is causing the problem.

Mrs Addams

Rb/ Htg,
can't work out why the boiler should neccessarily be on when using the shower, unless it is a Combi. If so why is there a diverter valve?
Or am I missing something? Just Curious!

I'm assuming it is a combi, a diverter valve is a valve in a combi which diverts the water to heat the radiator or heat the water, with a combi - water is always given priority you will not get HW and CH together, if the heating is on and you run the hot tap for a long period of time you will find the radiators will start to cool down.

A three/two port diverter valve is what you'll be thinking of which is found on a heating system again to divert the water to CH, HW or BOTH.

htg

I'm no expert but in my experiences of combis they need a certain minimum flow before they will work. When you turn the taps on and the hot water goes cold does it also drop to a lower flow level?

It's probably a control valve setting problem.
When the flow rate is increased to maximum, the pressure in the system has to fall as a consequence. Unless the control valve is set to keep the boiler firing at the lowered water pressure, the gas is cut off. This should be easy to fix, unless there's something wrong with your water supply pressure.
Is the stopcock fully open?

'When the flow rate is increased to maximum, the pressure in the system has to fall as a consequence'

eh ??? why ?? how ???


The CH and DHW sections on a combi are completely seperate, the MCWS pressure and the CH system pressure will not affect each other.


htg

Unfortunately I am completely confused by some of the answers posted.

Further experiments with the shower show you can get it to run hot but by a bizarre method. In fact the temperature control is almost working in reverse!

The less you turn the temperature control dial up, the hotter the water is now (hence it turns cold when you turn it up to the top). Whereas when it was working normally before, it used to be that the further you turned the dial up the hotter the water got.

And just to confirm, yes it is a combi boiler and it does have a diverter valve (as the excellent forum member [i]htg engineer[/i] states).

I thank you all for your assistance. I'm just going to have to live without the shower working properly because nothing I do to the stop cock or boiler pressure has any effect on things and I'm not skilled enought to try anything else.

When I can afford the new part that might turn out to be completely unnecessary I will let you all know how I get on :(

"Unfortunately I am completely confused by some of the answers posted."

I'm not surprised. The last few posts have diverted the thread into a discussion which has provides little help to you.


"Further experiments with the shower show you can get it to run hot but by a bizarre method. In fact the temperature control is almost working in reverse!

The less you turn the temperature control dial up, the hotter the water is now (hence it turns cold when you turn it up to the top). Whereas when it was working normally before, it used to be that the further you turned the dial up the hotter the water got."

Whilst that might indicate a problem with the cartridge I'm afraid I do not believe in coincidences. You've said that it affects hot water at taps as well as the shower so if the shower cartridge had a problem it wouldn't affect the taps. The fact that this started as soon as the boiler service had been done says that the service engineer needs to be called back irrespective of whether any blame is to be attached to him.


"I thank you all for your assistance. I'm just going to have to live without the shower working properly because nothing I do to the stop cock or boiler pressure has any effect on things and I'm not skilled enought to try anything else."

No you should not have to live without it. Get the guy back.


"When I can afford the new part that might turn out to be completely unnecessary I will let you all know how I get on :("

I'm not sure how you know which part to buy if you don't know what the problem is. Sorry to labour the point but you really do need someone to look at it for you on site. None of us can see it from behind the keyboard.

Best of luck.

Cheers

I think you need an RGI to check the gas pressures and possibly the diverter valve, when you turn the temperature control up and down, it will be allowing more or less hot water through, when you have it at the hottest setting the cold side may be fully closed and the water may be going through the combi boiler too quick, if the gas pressures are incorrect the water will not be heated adequately if you think about the time the water spends in the boiler and the temperature rise you're expecting you need quite abit of heat to achieve that.

I say possibly the diverter valve, because sometimes diaphragms in the diverter split and the water goes through the split in the diaphragm rather than forcing against it to operate a microswitch.


htg

"I think you need an RGI to check the gas pressures........."

Preferably the one that touched it last as these problem only started after he visited to do the service!

"Also it may be worth checking the shower filters.........."

But the lead post says this phenomena also manifests itself at the taps so really unlikely to be the shower IMHO.

Cheers