When the boiler is on full burner (using hot water) a loud sqeeking/alarming sound is coming from the boiler.....the boiler is a baxi 80eco combi. Firstly i thought it could just be the fan, so used little bit of wd40 to lubracate the bearings but it has'nt fixed the problem. Could it be the 3way diversion valve & how easy is it to change? Thanks Super Si!! :P

Super Si! Saving the wrld from gas explosions!!!, October 2009

sound like the dhw heat exchanger is blocked up you can take it off, run cold water through it shake it about till the black bit stop comeing out, refitt it should be ok now

erj, October 2009

wd40 tends to dry things out, it removes moisture, i would avoid it, get a proper spray grease or fan lubricant. Squealing/hissing on full flame is a pretty big sign that heat/ex is scaled up pretty badly but an engineer will be able to tell straight away location of noise and obviuosly check all gas pressures to make sure boiler operating as designed. One of them...need to be there type questions

ste, October 2009