HW cylinder back filling

[Andy Anderson]

I am working on a commercial premises with 2 HW cylinders, 1 supplying the kitchen and 1 supplying the toilets and various sinks. I am having Issues with the cylinder supplying the toilets (set at 2.4 bar) rising through the night to 4.8 - 5.0 bar. All the sinks have TMV3 under sink mixers and the cold is boosted cold water from a tank at the top of the building. I have proved the the cold supply through the regulator to the cylinder is not passing as I have isolated the inlet and the pressure still increases and we have fitted Non returns on the flow pipework from the cylinders but we are still getting a pressure increase through the night? Anybody have any ideas where to look next?

 

[Daveydub]

Is it expansion vessel/air gap problem so pressure rise is heat related rather than time related?