CH but no Hot Water

[leipere]

PLease help.
I have had a problem with my hot water for the past few months. THe pressure keeps dropping and therefore which I know has impacted this.
However more recently even when the pressure looks ok we sometime can't get even luke warm water. There doesn't seem a pattern to this. The heating is working fine.
Problems seemed to escalate after we turned the rads down slightly - have bled and checked for leaks.
Last night though I heard water in the back yard and when I checked there is now very hot water coming out of the over flow.

Can anyone give me an idea of what is wrong. A plumber mate is coming to have a look on Sunday but it is a long time between now and then and thought might be able to do something temp.

Thanks
Emily

 

[kevplumb]

give us a clue

 

[leipere]

sorry I should have added that it is a Vokera Excell.
Not sure if that helps.
If I can give more info so you can get a better idea please let me know.
Desperate to have hot water again

 

[kevplumb]

by the sound of it the boiler is over pressure and the relief valve has opened

what is the boiler pressure

 

[leipere]

At the moment pressure is around 2 but it seems to drop very quickly.

 

[gas4you]

hot water could be diaphragm, but due to age of this boiler I would suspect heat exchanger scaled up?

 

[kevplumb]

why would that lift the prv

 

[gas4you]

insufficient flow causes pressure to build up as it is heated up so prv will open

 

[Agile]

insufficient flow causes pressure to build up as it is heated up so prv will open

But if the EV is correctly set then that will easily absorb the small expansion from DHW use as its sized for the rads.

Tony