Hot water supply keeps going hot and cold

[seedsy4]

Hi,
My boiler has started playing up these last few weeks out of the blue. I have an Alpha C27 combi boiler, the central heating is working fine but when the hot water is running it keeps going hot for 20 seconds approx then cold for 10 seconds approx, then hot again and cold again etc etc. there are no warning lights on the boiler. No building work has been done or anything like that t mine, the only other problem and I don't know wether they are linked is that the pressure drops probably 2-3 times a week when the weather is cold, but its fine when it's hot?

Any comments or suggestions would be much appreciated

Thanks
Matt

 

[J_N30]

Without looking could be a few things but possible the plate heat exchanger. Is the 20 seconds of hot at a sufficient temp?

 

[seedsy4]

Hi thanks for the reply. It's red hot, it seems to be heating the water up fine but the burner seems to cut off for a few seconds every now and again and that's when the cold water comes.
It is quite strange really because it doesn't do it all the time. Sometimes when I run the hot water tap it works fine(hot all the time)