boiler problem

[bazza]

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

[htg engineer]

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.

[humperdink]

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

[bazza]

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