Problem with Boss Therm Mid-Position 22mm Valve

[cr0ft]

Hi all,

Was wondering if someone with more experience than me with Y-plan wiring could jump in.

HW working fine, no problems at all. 230v at grey wire when HW is off, 230v at orange wire when HW is on. All good so far.

The problem is that CH will turn on but will not turn off again until the power to the heating controls is turned off at the fused spur. There appears to be a backfed voltage of 120v or so on the white wire. I have disconnected the white and orange wires from the wiring centre to make sure it's not a backfed voltage from the boiler/pump. This backfed voltage is present when HW is off, i.e. 230v on the grey wire. As I understand it, there should be no way that 230v on the grey can backfeed to the white wire.

The backfed voltage is also causing the cabling from the SL on the room thermostat to the wiring centre (linked to white wire on motorised valve) to vibrate when the thermostat is calling for heat.

Anyone come across this before? The motorised valve is only 2 months old and was replaced by the previous plumber who had taken to swapping bits in and out trying to resolve the problem without testing the system electrically, apparently.

The customer cannot say for sure whether the problem started or not when the motorised valve was replaced...

 

[diamondgas]

Hi cr0ft .. the boiler and pump get their supply from either the orange from the diverter or the cylinder stat 'on'. I'd concentrate on testing them out 1st. if you disconnect the orange, turn cyl stat off and room stat on you should have 230v on the orange. Turn the room stat off and test the orange wire again. It should be 50-150v ...

 

[diamondgas]

Here's a bigger image or a link to it

 

[secret squirrel]

What was the original problem the customer had?

Did changing bits and bobs cure this problem or does that problem still exist?

Did the previous plumber alter anything else?

Has she got an invoice stating what work was carried out? this will give you a starting point.

Sorry, just very sceptical of customers.

 

[Leo21]

First thing id would be buy a Honeywell divertor, wire it in but don't fit. If it cures the fault happy days if not put it in stock. It sounds like the divertor to me.

 

[cr0ft]

Hi folks,

Thanks for the replies. I've been off on a holiday for the last week (unfortunately for the customer). Got an update from them this Thursday, the hot water (which was working fine before) has stopped working too now. It's all pointing to the mid-position valve being faulty in my opinion.

@secret squirrel, the original problem was the customer had to switch the power off to the programmer & wiring centre in order to turn the CH off. Turning it off at the programmer did nothing. Re the previous plumber, apparently they fell out. I've traced the wiring in the centre, from what I can see all appears to be properly wired. White from mid-position valve goes to output of room thermostat. Orange connects to HW on from cylinder thermostat via wiring centre. Grey connects to HW off on cylinder thermostat via wiring centre.

I don't understand why I'm getting a back-fed voltage of around 120v up the white wire though. I am sure that is what is causing the problem as it seems to be keeping the mid-position valve open.

I have spoken with the manufacturer and they are at a loss too, they suggested replacing the valve. I'm going to do what you suggest Leo21 and see how it goes.

Was just curious if anyone else had come across a similar problem before really. The only explanation I can come up with for a back-fed voltage on the white wire is a faulty PCB in the mid-position valve.

 

[Roger Welton]

The hot water is switched directly off of the cylinder stat not the diverter valve, just re-read your 1st post, I'd say cylinder stat would be my 1st port of call

 

[cr0ft]

Yup, sorry for not making myself clear. When I switch HW off and on at the programmer, 230V goes to either the grey or orange wire correctly, with the other wire going dead. I did check the cylinder stat too and it's switching off and on correctly, again confirmed by testing voltage on the grey and orange wires.

So far I've ruled out the programmer by swapping it, the room thermostat by swapping it. The cylinder stat works fine. Wiring appears to work fine. It's just the 120v or so being backfed on the white wire back to the room thermostat that I can't explain really. Everything points to the mid-position valve now, especially as the pump and boiler were working fine for HW up until last Thursday. I just don't want egg on my face by having to go back again to be honest.

 

[Leo21]

If the cylinder stat is switching, it's got to be the divertor. I've had all sorts if problems with them. 50 volts on to the synchronicity when under load and numerous other things.

 

[Roger Welton]

If you have a 3 port on the van just wire the head in to rule that out. Valve will stay in last port of call when shut down until power is removed from grey wire (this would explain it remaining in the htg position until power cycled)

Re the 120v has the cust done any DIY, screw through cable to room stat or similar?

 

[cr0ft]

Yeah, that's what I'm thinking. I suspect the 120v being back-fed somehow up the white wire is also what buggered up the room thermostat and original programmer too as neither was switching properly when I first went to look at it. I ended up disconnecting the white wire from the cylinder thermostat till I could get back to them. What they didn't tell me was that they had tenants moving in on the Monday I went on holiday = no heating for them all week!

Can anyone recommend the most reliable mid-position valve to fit? I'm thinking Drayton although all of the controls I've fitted are Salus so far. Will there be any compatibility issues between Salus and any other brand?

Done lots of S-plan wiring before, but as you can probably tell this is my first foray into y-plan systems.

 

[Roger Welton]

Honeywell, all 3 port mid positions are wired the same.

 

[cr0ft]

If you have a 3 port on the van just wire the head in to rule that out. Valve will stay in last port of call when shut down until power is removed from grey wire (this would explain it remaining in the htg position until power cycled)

Re the 120v has the cust done any DIY, screw through cable to room stat or similar?

I asked the exact same thing as there is a humming noise near the room thermostat when it switches on. That could just be 230v coming from the programmer conflicting with 120v coming the other way though.

To be honest I expect they have had a shot at DIYing it, not convinced about this previous electrician/plumber milarky.

 

[cr0ft]

Control problem fixed, mid-position valve was faulty. Great idea to check motor head first before fitting new valve

Now I'm back next week to fix a massive airlock in the CH return pipework on filling up, enough to stop the boiler completely. Ah well, at least the tenant has HW now and I have CH and HW at my house.