Combi boiler hot water fault

27 Mar 2012
Reaction score
United Kingdom
Hello all

Our boiler has a problem that when the shower is on sometimes the water runs hot for a few minutes then cold, sometimes just cold, it also makes a terrible banging/knocking noise when this happens. All the other hot taps seem to work ok. It's a Baxi Boiler, looks new(ish)?

Is it something to do with our shower? Or a boiler fault? An E code shows up E1 (and it says to reset).

Any help would be great please, thanks for reading my post
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Thank you for your help

I am not sure what model it just says Baxi on the front of it. The gauge is at 1.5 ish.

It seems odd that the other taps are fine it's justg the hot side of the shower
If all other taps are OK, then you have to suspect the shower is at fault.
Is the flow rate OK and the head clean?
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sometimes the shower lasts for longer than other times without the red light coming on on the boiler.

I suppose it could be a flow problem, not good. Are there any simple checks I can do to prove the shower is faulty before getting someone to fit a new one?

Thanks again for helping
Remove the head from the hose and operate the shower to test. If you give us the model, the E1 code may give us a clue as to whether its a boiler or a flow problem. I'm no expert on showers, but we have some very clued up guys on here who, I'm sure will be able to help.
The boiler needs a minimum flow rate to supply DHW and thats when its correctly set up. Not serviced or wrongly set can make it far worse.

Measure the flow rate out of the shower pipe, with and without the head.

Measure in litres per minute!

Thanks for your help.

I measure the flow rate from the shower, with the head on it's a lot slower. I noticed when I ran just hot and no cold from the shower the problem also didn't seem to happen.

So it's a flow issue? I'll try a new head when I go out this afternoon and see if it makes an improvement.

Why was the knocking noise happening out of interest?
sounds like shower is passing cold water into hot. fit check (non-return) valves on shower
how does a faulty shower cause a fault code on the boiler :D
come on people think about it. There's a problem with the boiler, get the model as nothing can be done til we know what boiler it is

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