Y plan heating problem low voltage

[stuartR1963]

Hi all I have the above issue, I have a hive active system with a worcester 18ri.
The problem is I am getting very low voltage coming from the orange wire from the 3 port valve approx 90v! this is when the heating only is selected and the hot water is satisfied. the boiler still appears to fire up and the pump runs. the pump is switched from the boiler as it overruns. about a month ago the cylinder thermostat was replaced. I can't help thinking its been miswired, the cylinder stat has a short piece of 3 core flex which goes to the wiring centre (brown,blue and Green & yellow)
I will do my best to explain the wiring setup, the pump cylinder stat and heating valves are all in the airing cupboard as you would expect all connected to wiring centre which is also in the airing cupboard. the boiler and programmer/receiver are in the kitchen. From the receiver two 3 core and earths run to the wiring centre
(in the wiring centre)
One cable contains from the receiver
Red=hot water on, this is connected to the brown which goes to the cylinder thermostat common
Yellow=central heating on, this is connected to the white wire to the 3 port valve
Blue=hot water off, this is connected to the grey wire from valve and the green and yellow wire which goes to the cylinder stat "2" terminal

Second cable
Red= boiler demand, this is connected to the orange wire from the valve and the blue wire which goes to the cylinder stat "1" terminal, the pump live used to be connected this terminal also but now has its separate live for overrun
Yellow= used to be spare but now supplies the pump
Blue= Neutral
earths obviously speak for themselves

third cable 3 core and earth went to the room thermostat this has been disconnected completely from the wiring centre due to the hive controller which just runs on batteries.
I would appreciate some help, the radiators are slow to heat up but that does not surprise me if the boiler only getting 90v, I am also struggling to understand how it could have worked on the old setup, when the pump wasn't switched from the boiler how the hell could it have worked before with only 90v?
I can only think the cylinder stat has been wired incorrectly, something isn't right, the cylinder stat in question is a honeywell L641A1039.
Hope this makes sense ,would appreciate some help
thanks

 

[AndyPRK]

What voltage is going into the brown wire into valve ?

Doubt it’s the hw stat

 

[stuartR1963]

What voltage is going into the brown wire into valve ?

Doubt it’s the hw stat

Hi, there is no brown wire to the valve, its a y plan, the valve has 5 wires g/y earth, blue neutral, grey, white and orange.

 

[AndyPRK]

Maybe the grey then lol.

What should happen is that the stat supplies 240v to the motor when it calls for heat.

When the valve has opened it should supply 240v to boiler on orange

So if what is coming out the stat is 240
And Going into the valve is could be the valves fault.

Try adding a link by the valve wires to prove it

 

[stuartR1963]

It may be the 3 port valve is faulty, the orange wire is 90v I can't get it to change, this is when the grey and the white both have 240v (heating only), so I don't understand why there is only 90v coming from the orange and not 240v?

 

[flameport]

With heating only selected and the thermostat set high to ensure that it is requesting heat, check the voltage on the valve wires. Should be:
240V between white and blue
240V between grey and blue.
If it isn't then the system is wired incorrectly or something else has failed.

If those are correct then you should also have:
240V between orange and blue
If not then one of the switches inside the valve has failed.

 

[ericmark]

I had similar problem with daughters old house, turned out faulty micro switch in the three port valve. Was a Sunday so could not buy switch, so swapped whole valve.

 

[bernardgreen]

so I don't understand why there is only 90v coming from the orange and not 240v?

The reading of 90 volts is almost certainly a false reading due to capacitively induced voltages on the orange wire. The orange wire is in the same cable as wires that have 230 volts AC on them and this will induce voltages on wires in the cable.

If you measure the voltage with a low impedance volt meter ( such as one with a moving needle ) then the voltage would be very much lower.

The induced 90 volts suggests that both ends of the orange wire are open circuit ( un-connected ).

 

[AndyPRK]

Clearly both ends aren’t disconnected as the boiler actually fires up when the heating stat is changed.

You could remove the orange wires and safely put it in a spare terminal block and measure the voltage. With ch on

 

[baldykev]

The orange wire is a switch wire only, tells the boiler to fire ,does not supply the main power for the boiler. have a look at this link.

when you say rads are slow to heat up on heat only does pipe from the 3 port valve to the water tank get hot ? as the valve may be faulty

 

[bernardgreen]

Clearly both ends aren’t disconnected as the boiler actually fires up

It is odd that a reading of 90volts can be found on the Orange wire as one end of it is ( should be ) connected to the boiler and/or pump. Either of those should provide a path to Neutral with an impedance low enought sink any induced voltage to 0v (relative to Neutral )

Stuart how exactly are you measuring the 90 volts ? Obviously one meter probe is on the Orange wire but where you putting the other probe ?

 

[bernardgreen]

Thanks to John Ward and Geoff Drage the mystery is solved. The sneak circuit in the valve across the terminals of the micro switch SW2 putting half wave rectified AC onto one end of the Orange wire and a control input ( high impedance ) at the other end of the Orange wire. So yes 90 volts on the Orange wire is possible.


image by Geoff Drage

 

[baldykev]

sorry for links but easy then me trying to write it all check from 6 mins on vid till 16mins explain how valve works

 

[AndyPRK]

Is the valve fully going over to ch I wonder ?

In which case the hw tank pipe would still be hot.

 

[ericmark]

As I said likely the micro switch is stuck however in the main we would change head not the micro switch. Although JW gives a good explanation on how it works, not all makes use that system, and with some you need to swap whole valve, others you can replace just the head.