Warmflow boiler problem

I was asked recently to have a look at an oil boiler that was giving off strange noises shortly after firing up.

Its a 90/120 indoor condensing oil warmflow boiler.
The circulating pump(located on the flow)is working fine as is the bioler interlock.
Their are three zones controlled with time/temp via motorised valves and all zones are heating up fine.
When the boiler fires up i can hear quite clearly the boiler start singing(kettelling)and even groaning similar to poor circulation whether all zones are calling or not.
Their is a auto-bypass fitted.

Any suggestiones??

Pache.

There is no obivous answer here, but a bit of investigative work should resolve it.

Firstly, I would test the sludge content in the system, i.e. with a TDS meter. This can often lead to a noisey boiler due to sludge particles trapped within the boiler.

Secondly, I would see how long it takes for the noise to begin. Does it happen immediately or does it only happen once the boiler has reached temperature. It is a large output boiler and perhaps the pump is only a 25/50. Minimum should be a 25/60 in order to get the heat away from the boiler quick enough. If happening immediately, then I would have a closer look again at sludge content or system design issue (see below).

Next I would check that proper boiler interlock is in place. Manually remove all heads from each zone valve and manually leave them all in the open position. The boiler could be firing and the pump circulating before the valve open and if so this is a wiring issue.

Lastly, check to see the ABV is set to approx 0.4bar. I would doubt this is the issue though and my money would be on sludge/debris trapped within the boiler itself and if so, a powerflush is the only answer. Make sure there is a good quality inhibitor put into the system afterwards such as Fernox F1.

Also, is the system open vented or pressurized? If ov, describe the locations of the pump, f & e pipe and the osvp. If pressurized, describe the location of the expansion vessel in relation to the boiler & zone valves.