Banging/ knocking on Puma 80 (perm pilot)

[DaiWelsh]

Hi All,

Fresh problem with my Puma 80.

I have scoured the forum but can't find a match, so here we go.....

Everything seems to work OK, but when demand is on CH, after a few seconds of burner operation a knocking develops which builds into a steady rhythm until the burner cuts out. Definitely too loud and regular to be normal.
Seems fine when demand is for dhw, when pouring bath etc.

fault seems intermittant in that sometimes the burner cycle is short and therefor no knocking develops, however when the burner cycle is long the knocking occurs, I am not sure but the long burner cycles do seem longer than usual although I have never had the need to judge its cycle time before.

The dhw and ch settings are both on minimum, the boiler output on the pcb is at around 3/4 (3 bed terrace house, 10 rads).

The red light on pcb indicating flow switch operation for dhw comes on and off as expected.

The pump and wax capsule in the diverter are both less than two years old, the system was also flushed and treated around the same time.

Any ideas would be much appriciated as I have the fear that this fault will develop into a real problem and it is mighty cold out there!

thanks all, dave.

 

[bengasman]

Could be that the pump is not getting 230V.
Apart from that:
1. Are you absolutely sure the waxcapsule was changed (correctly)?
2. Are you absolutely sure the flushing was done correctly?

 

[DaiWelsh]

thanks for your reply, bengasman,

The flushing and wax capsule were both done by myself so open to "idiot error".

The wax capsule was replaced using instructions on this site and the boiler has worked fine for two years since, and still does operate normally except the noise.

The flushing was done with mains pressue with one open rad at a time, after running the sludge remover through the system for a couple of days, again two years ago adn the water now runs clearish, little bit grey. All sentinel products used inhibiter and noise reducer.

Plus a correction to my first post as the boiler does exhibit the knocking when drawing dhw. The knocking has only been happening for the last three days.

Is the problem possibly a fouled up heat exchanger?

 

[DaiWelsh]

Have now measured the voltage at the pump (or at least at the connector plug nearest the pump and on the pump side) 240 V is the reading