Changing 230V switching to 24V

[RandomGrinch]

It does seem that way. Maybe this could help from Intergas? https://www.intergasheating.co.uk/app/uploads/2024/03/Ref-1_X-Plan-Leaflet.pdf

Thanks for finding the diagram.
It's actually a beautifully simple system
(Just to avoid any earlier confusion, the orange and grey wires from the zone valves arent connected to the 24V terminals).

Simply, if the H/W timer is on; it has opened the circuit on X4 terminals 9 and 10. If the tank stat (NTC) calls for heat, a DHW switched live is output on the mains voltage terminal 5 (through an overheat stat).
This drives the Normally Closed DHW valve open, providing HW flow to the tank coil.
When this valve opens fully, the grey and orange wire from it provide a switched live to the C/H Normally Open zone valve.
This valve is then driven closed, cutting off the C/H.
Any signal wires of this valve are unused.
The change in DHW temperature is managed internally by the boiler.

 

[RandomGrinch]

Just to add, with the Intergas X Plan wiring - it may be possible to keep a dual zone system and OpenTherm control, through the use of a specific controller.

A Honeywell Home T6R - 2 zone system has been mentioned in previous posts...

Opentherm on 2 zones installation

Hi all, I am about to get a new Intergas Rapid 32 Plus boiler installed. I need 2 zones and my original plan was simply to have 2 zone valves , controlled by my 2 Google Nest Thermostats as On/Off thermostats. However I came across something interesting page 26 of the boiler manual (refer to...

www.diynot.com

But that now seems difficult to get hold of.

This isn't a recommendation, but to prove they exist, here's an ESI dual zone, OpenTherm system...

CPC2ZP6COT - ESI Controls Support

2 Zone Combi Pack With Wi-Fi & OpenTherm

support.esicontrols.co.uk

Something like this could independently control the two C/H zone valves, whilst providing the OT output to the boiler
(Although, including the X Plan zone valves, you may end up with quite a few valves in your system!).