Noticed yesterday that the boiler made a couple of wdumff type noises and wondered as to the cause. Boiler is Worcester Bosch Greenstar 24Ri, powering a vented heating and hot water system. After the wdumffs, the boiler went into alarm mode with the blue indicator light flashing quickly. The noise *appeared* to be coming as much from the connected pipes as the boiler itself.
The system has 3 zones, upstairs heat, downstairs heat and HW. At the time of the problem, it was serving the downstairs heat only. As I have the hall rad off ATM (and all other d/stairs rads have TRVs), I thought it was the boiler overheating due to lack of flow. But, there is an auto by-pass valve in the airing cupboard - after the pump but before the 3 zone valves - which I thought should allow for this! When I noticed the problem I ran upstairs to check out the by-pass valve, and the discharge pipe was well hot!
Anyone any suggestions please?