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hi guys problem is wen on hot water only no problems ,but switch 2 ch n the pressure gauge goes shootin up to 3 bar n out the prv i figure either the pump or expansion vessel is at fault (hope its not vessel as boiler will need complete removal ahhh) but i switched boiler off n electrically isolated it then opened vent plug in pump which black water poured out n i rotated the shaft inside which turned freely then i put a multi meter set @ olms across the live n nuetral terminals n got a zero readin which cud suggest the pump bearings are worn out am i right in thinkin the pump is at fault or cud the problem b elsewhere ps boiler is a baxi instant 105e about 5 yrs old n there hav bin no extensions to the ch circuit THANX for any advise bazza

Sounds like it is the pressure vessel as the pump also runs when the hot water is on.

The pump running pushes a diaphragm and pin up which operates a microswitch. So if the boiler fires up, then the pump will probably be ok.

Do the radiators heat up ?

The fit the same pressure vessel you have to take the boiler off the wall, but an external pressure vessel can be fitted if you wanted to.

dont't know if you did but you need to remove the wires at the pump to get a proper resistance reading and if it is the model i am thinking of the pump runs for hot water as well as heating.

however it does sound like the expansion vessel at fault, what you can do is:
- drain the ch circuit - just use the prv as you will probably need a new one anyway BE SURE TO LEAVE PRV OPEN & attach at foot pump to the schraeder(car tyre type) valve on the expansion vessel & check the pressure - you should be able to see it with a black plastic screw cap looking down on the expansion vessel from the top
- if it is at zero just pump it up to 0.5 bar with prv still open
- then check that the valve is not passing with some soapy water
- close the prv & refill

if the pressure goes up & stays at 0.5 bar you are ok if not new expansion vessel required unfortunately - just remember you will probably need to replace the prv

thanks

THANX 4 reply much appreciated if i fit an external vessel am i right in thinkin i wud connect it on the return pipe close to the boiler also wat size vessel wud u reccomend using as a guide its a 3 bed. house 1 bathroom with 3 rooms downstairs hope this helps cheers bazza