Greenstar Wiring Centre not talking to boiler (or vice versa)

[slpn1]

I have a Worcester Greenstar 27RI compact boiler downstairs which is connected to a Greenstar Wiring Centre upstairs next to the hot water cylinder. The wiring centre talks to the boiler on an eBus connection. About a month ago I connected a Tado stat to the wiring centre on IZ3 in the wiring centre as instructed by Worcester tech support. It's a simple relay setup, stat bridges IZ3 which calls boiler for heat. Everything has been working perfectly up to yesterday.

I noticed that the stat was calling for heat but the boiler wasn't firing up. At first I thought the boiler had packed up, but calling for hot water fires up the boiler fine. The slightly confusing thing (to me) is the wiring centre only has a connection to control heating with a stat. There is no way to call for hot water (confirmed by Worcester) so you need to keep a controller connected to boiler (DT 20, photo attached) for the water and I had to set CH to constant ON. This controller is not the problem as I had a replacement turn up today and I still have the same problem.

The wiring centre is setup as S Plan exactly as in diagram attached and we have a standard 2 port system for heating/water. I have removed the Tado link on IZ3 for now just to eliminate that being the issue. I had an electrician here yesterday who tested everything and said everything is wired correctly and each individual element (pump, valves, etc) are working fine. He thinks the wiring centre needs replacing. When heat is called for either from the DT 20 stat or by bridging IZ3 no power is sent to open the valve on PZ1 or the pump on PZ3. Nothing happens, no errors, just nothing kicks in. The wiring centre flashes different error codes when it detects things like BUS not connected or cylinder stat not working. Everything is green and solid, I'm just not able to get it to kick in to open valve and in turn call boiler for heat.

I know the wiring centre can talk to the boiler as hot water is working and if I turn the boiler off the wiring centre flashes to say BUS is lost. The only slightly odd thing I've found which might be nothing is IZ1 is at 25v to neutral or earth even when the HW valve is closed. I would expect it to be zero, but not sure if a bit of leakage is normal on those valves?

Before I buy a new wiring centre which I have a hunch isn't going to work, any ideas what might be wrong or anything else I should look at?

Thanks,
Simon

 

[CountryFan]

Sounds more like the motorised valve not opening and making the microswitch. Put the heating demand on and try to move the lever on the Honeywell motorised valve, floppy or resistance felt?

 

[slpn1]

Sorry, I didn't get a email notification so I've only just seen this. The valves are both fine, the terminal that powers the valve to open (PZ1) doesn't get power when calling for heat. When directly powering the valve it opens and sends voltage back on the orange cable when it fully opens. Hot water has stopped working now so something has gone really funky. Everything looks fine on the boiler, boiler controller and wiring centre though.

 

[CountryFan]

When directly powering the valve it opens and sends voltage back on the orange cable when it fully opens. Hot water has stopped working now so something has gone really funky. Everything looks fine on the boiler, boiler controller and wiring centre though.

If the brown in for the PZ1 has stopped receiving voltage I’d say it’s either faulty room stat, programmer or loose connection.

 

[slpn1]

Thanks for your help. I had a Worcester engineer come and say the boiler probably needs a new PCB but can't be sure (will cost me £600 to find out!). I decided to take out the PCB to see if it had any obvious areas where it had blown. It looked perfect. Connected it all back up again and to my surprise everything started working again....almost! Now the call for heat is working, valves are opening, pump starts running, boiler starts to fire up. The problem I have now is that it can't ignite. It tries to light four times (I can hear the clicking) then gives up with the 5 second off, 1 second on code which is "No ionisation detection after ignition". I have tried resetting the boiler and same issue. I really feel the issue with the PCB was a bad connection but the boiler has been off for so long there is something I need to do to get it to ignite. I've checked the gas valve under the boiler. The screw is inline with the gas pipe coming in, so pretty sure that's on. The isolator at the meter is open and I can't see any other points it could be cut off. Any ideas to get the final bit working would be greatly appreciated! Thanks, Simon

 

[slpn1]

On the off chance anyone has the same problem, I got a 3rd party Worcester engineer round yesterday. He said it could be the PCB but wasn't sure. Quoted £550 and to try it with no guarantee of a fix. Once he left I removed the PCB to check for damage. It looked as good as new but I cleaned the contacts anyway. Put it all back together and nearly everything started working. Call to heat started fan, pump, valves opened but the boiler wouldn't ignite. Gave up after 4 attempts. Checked gas supply, condensor pipe etc. Was about to give up and get someone in again. Looked again today and I noticed the air intake pipe sat on the side. He hadn't put it back!. Opened up boiler, reattached air intake and voila, back in the warm! I have a mate who is a Gas Safe engineer coming tomorrow to give it a once over though just to make sure. Thanks for your help @Stuckinarut