3 port valves (Y plan system) weird fault

[Rossco B]

Hi Everyone
I have spent the last 2 days reading Diagrams and watching YouTube videos on Y plan systems and 3 port valves but I have not found any that have shown the problem I had which was that the Boiler got stuck on (pump running and heat circulation) making the hot water cylinder and rads hotter and hotter after turning the boiler off for a few hours then turning it back on and testing both the stats and Drayton control panel everything worked as normal this problem has happened before so I replaced the CH stat and Drayton control panel assuming that one of these was the culprit the Drayton panel did have a sticky relay but Now the problem has happened again I have focused on the 3 port valve and cylinder stat I feel the issue is with the 3 port valve as I-am told this is the first thing heating Engineers replace when this sort of problem happens.
Anyway The problem I had was that the CH thermostat was satisfied ,the HW Cylinder stat was satisfied and the Drayton control panel relays both HW and CH side were off (not calling) therefore after studying videos and drawings I can only conclude that the the diode in the 3 port valve somehow malfunctioned allowing the Grey wire which is permanently live to short over to the Orange one which fires up the boiler this would in my opinion explain the boiler going into a kind of run away mode. What I want to know is that is this a possibility? Otherwise I cant see anywhere else as to where the boiler could have been getting a live trigger from then held into a kind of run away mode?

 

[CBW]

Are you able to test it with a multimeter?

 

[Rossco B]

I would have to wait until the fault happens again,

 

[HERTS P&D]

Nothing like an intermittent fault!

But saying that, I would replace the valve, give the system a flush with new inhibitor.

Andy

 

[Rossco B]

I am going to replace the whole motor unit but just wondered if anyone has ever known the Grey wire to short through the valve unit to the Orange wire and cause a permanent live trigger to the boiler.

 

[CBW]

It doesn’t tend to short, but a sticking microswitch can happen and cause the boiler to fire up.

 

[oldbutnotdead]

Is this a new installation (or been worked on recently)- If yes then you can get problems with miswired control setups latching on (favourite on 2 port valves is to use the valve motor supply to feed the microswitch)

 

[Rossco B]

No it’s about 7 years old not been modified or anything recently.

 

[oilhead]

If the 3 port valve is a Drayton unit like the rest of your system, Then you have done well for 7 years. The MA1 actuator can do many silly things, one of which is that with all power off, it will return to normal, and work perfectly when switched back on, until you have heating only selected, when whatever state the controls are in, it will not return even with just HW selected. I have customers where the actuator has been changed every 2-3 years.

 

[Rossco B]

It doesn’t tend to short, but a sticking microswitch can happen and cause the boiler to fire up.

That can only happen if one of the Drayton panel relays and a thermostat is calling otherwise as I said the Grey wire is the only one live and the only possible electrical path is a residual current through the diode to the orange to the boiler

 

[CBW]

That can only happen if one of the Drayton panel relays and a thermostat is calling otherwise as I said the Grey wire is the only one live and the only possible electrical path is a residual current through the diode to the orange to the boiler

No it can happen when there is no call for heat, as the grey is permanent live, so if the switch is made without a demand, unless the power is off, then a demand will be created without controls calling.

 

[Rossco B]

If the 3 port valve is a Drayton unit like the rest of your system, Then you have done well for 7 years. The MA1 actuator can do many silly things, one of which is that with all power off, it will return to normal, and work perfectly when switched back on, until you have heating only selected, when whatever state the controls are in, it will not return even with just HW selected. I have customers where the actuator has been changed every 2-3 years.

That’s similar to what’s happening it just bugs me that it’s doing something that should be impossible current shouldn’t be able to travel the wrong way through a diode unless the power from the grey is shorting through the mechanism of the valve somehow.