Shower giving a mixed hot and cold water when i use hot watr

[shocksl]

hey guys

i have a combi boiler which has central heating and water connected to it from the basement.

when I used to shower with Hot water, it used to be more or less at the same temperature throughout (hot). However now when I shower with hot water, it's hot for 20 seconds and then goes cold for 10 seconds and goes back hot and keeps repeating.

I dont know why this is? I have set the combi boiler to preheat mode, like it always was. so i dont know what the problem is??? it wasnt like this a few months ago1

hope someone can help.

 

[ianmcd]

can be quite a few things and most cant be repaired without opening the combustion chamber so afraid you will have to get a RGI in to check it out for you

 

[shocksl]

wot few things can it b

 

[calorific]

Before narrowing it down to the boiler, is there any fluctuation when you are just running a hot tap?

 

[shocksl]

yes it goes hot, and then cold for abit, back to hot again

 

[45yearsagasman]

That could be a blocked plate heat exch, among other things, but as you don't give the make model, and just call it a combi boiler what chance do we stand.