boiler vibration

[gedtodd]

Hi all, recently replaced the expansion vessel on my baxi 28 platinum, flushed system and added inhibiter, have now noticed that theres a strange vibration which comes on when the gas fire-up starts, then disappears, temp reachs 78 deg, falls to 57, but reappears on next fire-up, this is only on call for heating. Does'nt happen when hot water is on demand. Suspecting the pump, but your advice greatly appreciated,
regards, Ged.

 

[LIFES A GAS]

Would not think it would be the pump as not doing it on HW, the pump will run at the same speed on heating or HW, try turning off all the rads except one, then run heating, any difference? Was the expansion vessel pressure checked before installing it?
Martin.

 

[gedtodd]

Hi Martin,
sorry have not replied sooner as only got back from working away today,( sat), i did check the pressure of the expansion vessel as i was on a site whereby quite a few of the 442 units i installed had lost their charge. i closed all the rads bar one, and on start-up it was fine. opened second and vibration started again. closed this and upon next fire up it vibrated. this only lasts for say 7 seconds, and sounds rather like a bearing fault, the way it whirrs. after 18 seconds of a 2mins 50 seconds heat up to 78deg c, there is a definate clunk noise from the boiler, rather like a switch, but then everything sounds fine until the next fire up?
Thanks for your advice and help in advance, ged