Our hot water began to play-up when the boiler was just over a couple of years old and the problem continues to this day (3 years down the line). Annoyingly, we only changed the old one (10 year old Vailant combi) after repeated attempts by BG service people, including replacement of most major component, failed to fix exactly the same problem.

The problem is that the hot water is not reliably dispensed. When not produced on demand, the boiler is not firing-up properly. It makes a half-arsed attempt, with whirring of exhaust fan and a brief puff of steam, but at the tap, the water is cold or lukewarm. Sometimes, though, it plays ball and the hot water is fine.

Now here's the thing; if water is drawn simultaneously from a hot outlet and certain cold outlets and/or a second hot outlet, the boiler can usually be made to fire-up and away we go. In some cases, closing off those additional outlets causes the hot water to wane.

In the light of the observations described above, it seems to me that there might be an issue with water pressure, but it's not that the flow rate is too high for the boiler to heat the volume passing through the heat exchanger. I say this because i) draw from additional hot outlets can remedy it, ii) when it happens, the boiler isn't firing properly and iii) if anything, the problem tends to be worse in warmer weather.

I did, in fact, check our water pressure and found that while it was rather high, it fell within acceptable operational range for the boiler. Regardless, I wonder whether it's worth trying an adjustable pressure limiting valve on the boiler inlet. I'm more open to a sporting chance of a pragmatic solution rather than a dead certain lengthy investigation!

What do you think? Worth a try, or total waste of time?

Cheers. Terry.