I have a Worcester Heatslave RS 15/17 combi boiler on a closed system. No water tanks at all. All of the taps in the house (with the exception of the external 'garden hose' tap) are mixer taps.
I am informed that I have strong mains water pressure. Welsh Water's service level is 7bar. I have no way of checking. We live at 220m altitiude, so not sure if the would affect it.
Problem I have is that after a tap is closed, no matter how long it was opened for, the boiler appears to take (a little) water and (if it is set to be on, it fires). There is also an obvious clunking sound in the boiler. The effect of this passage of water is felt throughout the system. EG is the loo is flushed the radiators creak (as presumably the pressure in the system is changing momentarily).
The boiler is only 2.5 years old (I didn't have it installed) and at the 2-year point the three-way Honeywell diverter valve failed. I'm led to believe this should last about 8 years.
First plumber (who replaced the Honeywell) said we had loose pipes. This doesn't make sense as the effect on the boiler is apparent throughout the house (ie all of the pipes would have to have been loosened magically the day the new valve went in).
Second plumber reckons it is back pressure and that fitting non-return valves on each feed to each mixer tap would stop hot water being pushed back into the boiler by the force of the mains. He says that there is a spring on the diverter valve which only springs one way. The back pressure is forcing it to go the other way which is why the first valve broke so soon ( I recall plumber1 saying that the flap which did the actual diverting got stuck and wouldn't move as required, so this fits in with plumber2's theory)
This sort-of makes sense to me, but for the fact that closing external tap (located next to the boiler, but on the outside of the house) also triggeres the same reaction in the boiler.
Do these symptoms and theories ring true / false with anyone?
If relevent system info: boiler as above, bungalow, 10mm pipes, 2 rads with TRV, 6 rads without TRV, 1 zone controller, kitchen and bathroom mixer taps, bath/shower mixer tap, 1 external tap. Cold water pressure seems good and the shower gives strong flow.
Thanks for your comments.
dave.