Hot water system - noise and not enough hot water

highwalker

Investigation last night managed to reveal that the expansion vessel on top of the thermal store was out of water: so, either the inlet was blocked up (seems unlikely at mains pressure), or the ball valve inside it has got a problem - e.g. grit in it. This could explain some air getting in as the expansion emptied. Topped it up manually to see what would happen - water still in there. However, noise events still present, if perhaps sounding fractionally less harsh.

Alex1983

It’s quite common for the cold feed from the header tank on top of the boiler mate to block, if your header was empty, I wonder if there is airing in the top of the store and it can’t refill because the cold feed is blocked.

highwalker

Thanks. Conclusion is now that the feed from the expansion tank to the thermal store was blocked, but more importantly the circulation pump had/was dying. This led to cavitation in the boiler that resonated upwards plus variable temperature hot.. Pump now replaced and all running quiet so far.