Fixing hot water supply problem (boiler expansion vessel..?)

[Atultomar]

Hi

I have a Britony combi se 80 boiler which is connected to an indirect & unvented megaflow cylinder (heatre sadia). Central heating seems to be working fine when it runs....

However, when the hot water is expected in kitchen and bathroom, it's not a regular supply. The water temperature remains hot for about 2 mins and then again turns cold.

On the other hand I have observed that the boiler is losing water pressure every now and then. There are no leaks around the piping and radiators. When I pump in additional water pressure, it continues to work on central heating and in few mins for the hot water supply as well but not consistently on the temperature to the hot taps and shower.

I read some issue with the expansion vessel in the Boiler but not sure about it.

Any help with right skills and knowledge will be highly appreciated...

Thanks....

 

[MANDATE]

When a boiler loses pressure it is related to a leak. the leak may be in the pipe work or radiator valves, but usually related to the expansion vessel.
The vessel is supposed to contain 'air' which gets compressed, but insufficient 'air' pressure can send the water pressure quite high to the extent the pressure relief valve opens at 3bar to release the pressure and the closes again.
Sometimes the PRV does not close properly and leaves a small leak, so the pressure after having been correctly set gradually drops. the time to drop could be anything from few hours to few days.
So check the PRV and replace if found to be leaking

 

[ianmcd]

It has nothing to do with your boilers expansion vessel that you only get two mins of HW then it runs cold

 

[MANDATE]

The problem relating to hot water sounds like a diverter valve sticking.
The 'hot water heat exchanger' is supposed to heat cold water passing through it by using the boilers hot water. If the diverter is restricting the flow of the boilers hot water, then it can't heat the cold water coming in.