Until last week I could turn the tap on the bath to full and out would gush hot water. Now, to get near the same temperature water, I can only turn the tap on to perhaps 20%. This means it takes a very long time to run a bath.
The settings on the boiler - an Isar HE30 - haven’t changed, and I’ve checked that the temperature is suitably high. And it does produce hot water when the flow is reduced. The gas flame is lit. There’s a CO detector which has not gone off.
How old is the boiler? How hard is the water? Generally, after 10-15 years they recommend to throw the old boiler out and buy a new model because it will be full of chalk inside and it’s not easy to de-calcify (because of the pressure).
The water runs off granite. I’ve done some digging and it seems that someone had exactly the same problem except that in their case the pressure was too high - it needs to be below 1.5 bar and this is 0.9.
