boiler over heating and hissing

[zacksons]

its potterton combi 80

When I switch the boiler the water heats up ok and the heating starts as

well but after some time there's a hissing sound and steam comes out

from the top of the boiler.

I checked the switch and thats working fine.

So please help as we have no heating and no water

thanks

 

[DarkInferno]

are your radiators getting hot?

check the pump, as you appear to be kettling.

 

[zacksons]

The radiator heats up only half way and it seems the water thats returning does not heat up.(its not the temp it should be)

 

[DarkInferno]

ya... check your pump you have a definate circulation problem, also run through the obvious checks, that you have water in the system, etc.

 

[zacksons]

but why would it still overheat if we do not have the CH on only the water on

 

[DarkInferno]

I don't have the diagram for a Pott Combi 80 to hand... nor have I worked on one for months.. (a picture would help tremendously if possible)

Do you get the hot water? have you checked the pump? do you have a DHW heat exchanger? is the diverter opperating correctly? do you have a diverter? Is there an water in the system?

 

[DarkInferno]

A picture of the internals btw, I know what a white box looks like,

 

[kevplumb]

the hot water demand switch is stuck

 

[DarkInferno]

possible.. but then it wouldn't kettle unless he turned the water on and back off (unless its stuck fast of course.)

and not at all while there is DHW flow.

 

[zacksons]

Thanks I'll check that

 

[zacksons]

If I keep the water running the temp gets very very hot and when I switch the tap off the flame is still on and the water keeps heating and if the tap is still off the boiler starts to hiss and the steam comes out , if the water keeps running it almost gets boiling hot.

 

[DarkInferno]

then kev is right on the money