Who stole my volts?

Potterton Promax,pump not fed from boiler.
2 ACL zone valves controlloed by cyl/room stats.

boiler and pump not going.
CH ON 240v into wiring centre.240v to CH zone valve via room stat.Valve opens then arm on valve " rocks" back and forth. Got 240v permanent live to switch.When valve opens only get 105v on switch side,hence only 105v to boiler and pump.
DHW ON exactly the same scenario as per CH valve.
Disconnect either zone valve and the result is the same. 105v only to pump and boiler.
One dodgy m/switch ok.But 2? On 2 year old house.
Also checked neutral to earth on pump. 105v which is totally wrong.But normal at boiler.
Used 2 multimeters cos thought first may be faulty multi.
Bit puzzled?
Maybe looking into wiring centre for too long trying to work out what the chuffin sparks have done( why the F can`t they label things) made my head hurt.
Has the neutral scarpered with my volts?

Paul

Valve arm shouldn't rock back and forth. I assume that the sparks have not wired it in the industry standard 1 -10 (12) wiring block then

Agree arm shouldn`t rock back and forth.If it had been wired incorrectly from the start wouldn`t this problem have surfaced earlier?
Not going to throw parts at it in the hope it resolves prob.I don`t work that way.

Paul

I'd be looking for a broken/faulty neutral