A couple of weeks ago I refitted a radiator in our bathroom after it had been tiled. Coincidentally, during the back end of last week I noticed a knocking sound at the same time as I could hear water being pumped through the radiators in the house. I wasn't concerned as I thought maybe some air had got into the system (it is a sealed system with a 8 year old Saunier Duval Thelia Twin combi boiler) and I would go around the house and bleed all the radiators. Last night, the knocking became continuous and even louder and I now realise it isn't coming from the pipework or the radiators it is coming from the boiler but is being amplified through the piping so that it can be heard throughout the house. The noise appears to be coming from what I think is the pump which seems to be an integral part of the boiler.
The noise is a regular loud knocking sound and stops when I switch of the boiler, but starts when either the hot water only or heating and hot water settings are selected. The radiators are still warming up and the water is still hot so everything appears to be working okay apart from the loud noise which is so disruptive that we had to turn the boiler off last night in order for us and our children to get any sleep.
Our heating system is insured but an engineer won't be out to look at it until Thursday, and then I suspect we will have to wait another week while they get whatever spare part is required.
If this is a mechanical problem with the pump is it likely to be dangerous to leave it on? Is the problem likely to be the bearings in the pump or is it possible that trapped air could cause this noise? I ask this as if it is a problem with the pump I'm surprised that the radiators all around the house are still hot i.e. the pump is still working.
I would appreciate any suggestions on what the problem might be and anything I could do to fix it or minimise the noise before the engineer arrives later this week.
Thanks.