Worc/Bosh Highflow 400 electronic OF, terrible noise on HW

[Xarlie]

The boiler was working fine before I drained some water from the system down to about mid way on the boiler to fix a leaking joint above that level.

I fixed the leak and refilled the header tank. I ran the boiler to let trapped air escape to rads, air vents in boiler and up to the header tank. The result is that now the CH is working fine. But when the boiler heats the Hot Water bank there is a terrible continuous loud whine which eventually stops when the required temp has been reached.

The whine is made when the boiler fires up to heat the HW bank. The pump runs for a longer duration than the burner runs to heat the water. Only when the burner operates does the boiler make the whine. In other words, it does not appear to be the pump that makes the noise.

I believe some air is in the HW loop, but I cannot see how to remove it. The auto airvent on the heat exchanger has been letting air out as it should, but not all of it, it appears.

I have bled the pump.

Boiler is two years old and has furnox.

Any suggestions welcome - other than to replace the boiler!

 

[nickso]

you say you have a header tank....bad move on this boiler IMO. what colour is the water that came out of the boiler when you drained it?

 

[Xarlie]

Thanks for your reply.

The header tanks satisfies the makers specification wrt height, but I can believe that to be optimistic!

The drained water is clear with a slight grey colour, is the answer to your question

rgds