Hot water priority

[jk89]

Hi

My setup:
3 zone valves - upstairs heating, downstairs heating, hot water

3 BDR relays, one to fire boiler, one to open HW valve, third opens both heating zone valves at the same time.

Oil fired boiler, no modulation or opentherm.

I have a question on the hot water priority setting. Is it correct that if hot water is scheduled on, then the heating zone valves should not open during this time? Bedrooms are overheating early in the morning during the half hour that the HW is on. So either the hot water priority is not working as it should, or the upstairs heating zone valve is not closing correctly, allowing hot water to pass though when the boiler is firing and got up to a higher temp than the rest of the night?
Any info that could help with the troubleshooting would be much appreciated.
Also, advanced load scaling is set to normal, would it make any difference setting this to partial?

Lastly, does hot water overrun come into play with a non-opentherm system like mine?

Thanks in advance

[Richard]

Hot water priority and the overrun only applies to OpenTherm systems.

[jk89]

Thanks for that.

Any advice to help reduce rooms overheating when the hot water is on?

[Richard]

Thanks for that.

Any advice to help reduce rooms overheating when the hot water is on?

Maybe schedule the hot water away from heating timings?