boilermate 11 buzzing noise

Hi, I hope someone can help. Last week our boiler mate 11 started making an unbearable buzzing noise. The noise could also be heard from the boiler in the kitchen but wasn't as loud. A plumber changed one of the pumps which looked worn out when he showed me. However when he put the new pump on and fired the system up then the delay timer control board packed in and started to vibrate loudly and burn. I ordered a new delay timer and fitted it and it seemed okay at first but now everytime the hot water is requested for the heating or hot water out of the taps, the buzzing returns when the boiler mate kicks in. It's not as bad as it previously was but the buzzing is still bad. Any ideas what this could be? The hot water and heating seems fine, just the buzzing noise.

Make sure you fitted and connected the new board ok.
And it may now be the other PCB (pump drive board)
Both are in a hot place
And both may be the same age etc.
Very often I recommend fitting both at the same time.
More so to avoid a second call out for the customer later
Mike

Thanks for your reply Mike had new control board ready to fit but plumber has been round today and said that it's the pump that's making the noise as it's struggling to pump water around the system. He specified it as a kettling noise rather than a buzzing noise. To me it sounds like there is a wasps/bee nest.

We had a towel rail fitted in our bathroom around two year ago but a year ago is corroded and started leaking. When draining the towel rail to replace it, it looked like thick gravy. Could this be causing the system to clog up and ultimately that's why the pump is struggling to pump water and making the kettling noise? Do you recommend a product that can be used to clean the system or cost wise are we better off buying a new boiler? It's disappointing as the water and heating is hot working when required, it's just the kettling/buzzing noise that is irritating and I think it could potentially stop us from selling the house as it is currently up for sale.

Many thanks in advance for your help.

Well first thing I would do is;
Take white cap off top tank.
Drain some water from the unit, to ensure the unit takes water from the top tank.
If all ok then I would drain the unit.
See what it is like.
If really bad put some cleaner in 1 litre to every 100 litres.
Fill and run the system, noting any changes in performance / noise etc.
Mike

Thanks Mike, checked and feed and expansion tank is filling up and working as expected and both flow pipes aren't blocked. If i put some cleaner into the system, can i take the cap off and put it straight into the feed and expansion tank?

Thanks in advance

Yes it goes in there.
BUT
You must drain the unit and empty the top tank.
Drain for another 5 minutes.
Turn off drain.
Put in cleaner.
Which will go into the unit.
Add water to top tank.
Let that go in too.
Turn water on and fill ensuring unit is full.
Let the cleaner do it's job.
Mike