Got home tonight and could hear the pump is noisy again - not a loud whine but the "cavitation" noise... ? Here is a quick video of it, not sure how easy it is to make out on the recording because it does tend to exagerate how loud it is - it's certainly quite audible when opening the cupboard door but not that loud. Flow temperature was about 60-65 at the time and the boiler hadn't fired for at least 10 minutes.RichardW wrote:3. By the sound of it the boiler stat is on the way out too if you are getting 85C at the pump with it turned down - do you get kettling in the boiler when you turn it up? It's unlikely you are getting vapour in the pump - it wouldn't just whine it would cavitate and sound horrible before it got to that stage! More likely it is suffering a partial seizure (see 1 above)...!
In person it sounds like cavitation in the pump to me, maybe with a touch of bearing whine when you get a bit closer ? All the noise is coming from the pump and the surrounding pipes (including the ABV loop that you can see running above the pump) and listening with a screwdriver confirms it. No noise from the boiler heat exchanger at all!
Knackered pump, air getting in somewhere in sufficient quantity to cause cavitation, or both ?! All the radiators were bled yesterday - no air in any downstairs radiators but a small quantity in the two upstairs ones.