3 port valve

[truffle pig]

Hi, got an issue with a Y plan system. after the heating has stopped calling for heat I am getting around 30v on the CFH at the boiler - its coming from the orange on the zone valve and also back feeding the white (CH on) with the same voltage. it only does it with the HW off (so 230v down the grey from the programmer. the plumber has replaced the programmer & room stat before calling me ( all wired correctly) and I have replace the zone valve head - no difference. The programmer / tank stat and room stat all appear to be switching correctly, and there is no voltage present on the neutral. anybody else come across this? Back there tomorrow to test wiring etc

 

[ProDave]

It sounds like the boiler "call for heat" input is way too sensitive and being triggered by a low stray voltage. I would start by connecting a snubber across the call for heat input

 

[truffle pig]

It sounds like the boiler "call for heat" input is way too sensitive and being triggered by a low stray voltage. I would start by connecting a snubber across the call for heat input

Thanks Dave, I will give that a go. the system has been working fine for the last 8 years, not sure why it should change now

 

[SPECIAL LOCATION]

Have you split the orange from the valve, and the "water-on" feed from the cylinder stat, (at wherever they join before feeding the boiler CFH), to confirm 100% it is coming from the Valve orange, and not the Cylinder stat water-on, (whatever colour it is?)..

Remember..
"Water On / Heat Off" is the default position where the 3-port valve doesn't need to move.
(held in the home position via the return spring, no trigger voltages required, So the boiler CFH bypasses the valve).

"Water On & Heating On" has to stall the 3-port valve in the mid-position.
(only one voltage trigger from the heating thermostat, out to CFH via the valve orange).

"Heating On / Water Off" has to drive to motor to the furthest position.
(two voltage triggers from heating ON and water OFF, out to CFH via the valve orange).


How long is the cable run run from cylinder to valve/control centre box? Could this be a source of phantom voltages?

Whenever I encounter "strange" happenings with heating operation, I normally start splitting off bits of the control wiring, to ensure I'm not chasing my own tail up a wrong path.

I also sometimes use a bog-standard pendant bayonet lamp holder plus flex, with a GLS lamp wago'd across key points to verify the expected voltages are where they should be... As it can save a load of faff sticking meter probes in various screw terminal connectors trying to work out what's happening.

I presume this is the same physical boiler for the whole 8 years?