Noisy central heating boiler

[pilsman154]

I have an old Servowarm central heating boiler that makes a very loud rumbling noise for at least 30 seconds every time it is switched ON. After the 30 seconds the noise dissapears and the system runs O.K. I have bled all the radiators but the problem still persits. Can anyone help?

[leylander]

As you say it is an old boiler , last year I replaced my THIRTY
YEAR OLD boiler and cavity wall insulation installed with the aid of a government grant I cannot believe how much my gas bill is reduced (and I got a free three year full system cover as well)

[gasman]

You may have bled the radiators but have you also bled any other air release valves at the boiler and cylinder and maybe also at the highest spot in the loft aswell depending on the system.

[burnhal]

Had a similar noise a few years ago on my old system- the pump that circulates the water in the system was slowly siezing up. Took a good few months before it finally died the death but effect was similar- loud rumbling for up to a minute at every switch on.