simonp wrote:OK, now I'm very confused... whilst I was running the descaling solution through in several lots and 10 minute soaks I was getting flash billing out of the group as I ran each lot through. Now it is flushed and back running as normal it is back to coming out cooler with no flashing. The outside of the group only measures just above 70C. Not sure where to go with this now...
If the group is significantly cooler than normal whilst the boiler pressure (and, therefore, temperature) is normal then either there is a restriction in the thermosyphon flow or scale on the walls of the heat exchanger is reducing it's efficiency. If you are lucky it may be a piece of scale partially blocking the thermosyphon pipework which can be dislodged. Otherwise a more thorough descale of the boiler/heat exchanger/thermosyphon pipework would seem to be necessary.