No hot shower

[jedforest]

We have a Worcester combi boiler. The ch works fine, and there's hot water in all the taps - the problem is the shower. It works only when we have the ch on. Without the ch on, it's either stone cold or at best we get a couple of minutes hot-ish before it goes cold. It's a Mira mixer shower. We've had Mira shower guys out - they say the problem is the boiler. So we had heating engineers look at the boiler - they say it's the shower at fault! So far we've spent over £200 and we're no nearer a solution. Any ideas please?

 

[Puddle]

Firstly what model of worcester is it,so we know if it has a diaghram to operate hot water mode or not
But few checks,remove shower head
Does shower get hot or does boiler come on when you turn shower on
As taps getting hot Ok.turn shower on with taps running does shower get hot
Turn kitchen cold tap on half way,does shower get hot

 

[jedforest]

It's a Worcester 28i Junior. Just done your checks. If hot water on anywhere else in house we can 'take' some of it to the shower. But if no hot water running elsewhere and no ch on, then the shower either refuses to ignite boiler at all or it'll work for a minute or two (we can see boiler light come on) and then it'll go off.

 

[Puddle]

so are we saying with hot tap turned on slightly to assist flow the shower will run correctly ie hot
If so sounds like flow switch problem on boiler,as hot water pruduced through main heat exchanger on this model
If still not working would point to faulty cartridge or non return valve on shower letting cold through,however if this was the case taps near shower should not get hot also

 

[payney1974]

Seems showers not pulling enough HW for DHW flow turbine to register on worcester.

 

[jedforest]

Thanks a lot for your thoughts. Yes, I just tried it - if we turn on the bath or kitchen tap till it's running hot then turn it down to a trickle we do get a hot shower. So you reckon it's a problem with the flow switch on the boiler? Do you think we should get a different firm in to sort it, to the firm that came out (twice) and didn't diagnose that??

 

[stevetheplumber]

try the shower without the head attached if it works then its the flow thru the head thats causing the problem either descale the head or get a larger one

 

[Puddle]

Thanks a lot for your thoughts. Yes, I just tried it - if we turn on the bath or kitchen tap till it's running hot then turn it down to a trickle we do get a hot shower. So you reckon it's a problem with the flow switch on the boiler? Do you think we should get a different firm in to sort it, to the firm that came out (twice) and didn't diagnose that??

Well I do not know the firm that came out but if you have paid them money and they are reputable they should come back to sort out ,putting some of what you have paid towards final invoice,give them a ring ,now you know more about the siduation and go from there.

 

[LIFES A GAS]

Have you got a restriction in the shower head or hose, sounds like you have as the flow is not enough tofire up the boiler, you need a hose & head that are suitable for combi or power showers, many cheap replacement hoses have a very small bore, same thing with shower head or is it a blocked filter in the mira shower valve? as the boiler seems to be working OK otherwise.
Hope this helps, Martin.

 

[jedforest]

Thanks for all your input. One last question...I've taken the shower head off (it's pretty big - 10cm diameter) and there's still no hot water. So, given that the flow rate is the problem and the showerhead doesn't help - can the flow rate be increased on the flow switch in the boiler?

 

[LIFES A GAS]

If the boiler was the cause then none of the taps fully open would cause the boiler to fire up, clearly you can get the boiler to fire by opening a tap slightly while running the shower - yes? I would suspect the shower mixer is the cause of the restriction, it could have a filter/strainer that has become partly blocked or your isolation valves may not be fully open, check these first but as I say it's not the boiler as it works perfectly with other taps.
Martin

 

[jedforest]

Aw no! We're back to square one! To the great 'Is it shower or the boiler?' question. We had the Mira guys check the (new-ish, only two years old) shower a couple of months ago. They checked and re-greased the mixer valve and assure us there's no problem with the shower! Most replies here seem to suggest it's a flow problem. The boiler definitely works fine EXCEPT when we use the shower ONLY. If we use the shower in combination with another hot tap running anywhere in the flat or with the ch on, the shower's fine. So, we're kinda persuaded it is a flow problem, I want to know if that can be adjusted (increased), and how...

 

[RoryD]

Had a similar prob recently, thought same as puddle...anyway cut a long one short, the heat exchanger was filthy / Sooty, which was insulating it from the flame. When other taps are turned on the flowrate will be reduced overall which will be the same as turning one individual tap right down...which obviously allows more heat transfer. Make sure the engineer checks inside eh?