Combi boiler noise from hot water system

[jtrssn]

Our Ferroli Optimax 25 C combi boiler has recently started making a loud noise (a sort of low pitched whine/rumble) whenever there is a demand for hot water. The noise starts about 15sec after any hot water tap in the house (including the shower) is opened and lasts for about 30 sec if the tap is left running. After that the noise gradually subsides and is silent while the tap runs. If the tap is closed before the noise stops the noise continues for 5-10 secs. The noise can be heard throughout the house and even outside but is loudest on the landing next to the boiler. There is no noise when the central heating comes on.
The engineer who installed the system and services it annually is mystified and has nothing to suggest.
Can anyone help please? We are getting quite anxious about it.

 

[oldplumber]

try cleaning the plate heat exchanger if its blocked it may be causing the main heat exchanger to boil/kettle as not enough water is circulating thro it when heating the hot water circuit, only a thought cannt be sure as havent suffered this fault on hw system to be able to quote positively if im right.

 

[jtrssn]

Thanks for the suggestion oldplumber.

The boiler has just been serviced so I am assuming the heat exchanger was cleaned. Maybe wrongly?

 

[oldplumber]

heat exchangers arent flushed thro on a service, have a look at your boiler manual to see what happens in a service. is there any inhibitor in your heating system, if not pop some cleanser in for 2-3 weeks, flush the system then add inhibitor, this should have been done and may clear up the problem without whipping out the heat exchanger first.

 

[jtrssn]

Thanks for the suggestion, I'll give it a try.