Vaillant Ecotec plus 612 system boiler problem

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Hi,

I have the above boiler, was commissioned by gas safe engineer just over 5 years ago and has been faultless since until now I have a hive system controlling heating (usual radiators) and hot water and a unvented HW cylinder. All wired up on S plan I believe - separate valves for CH & HW.

Over the past few days I've noticed the house getting cold when the heating is on and when checking the Hive says 'heating' but the boiler is doing nothing. Turning HW on also makes no difference. I can hear and see the hive controller light up the heating and hot water lights and can hear the relay(s) clicking as usual when it does. Looking at the 'Live information' it says 'No Heat Demand:Controller' on the boiler. On a few occasions this has fixed itself by powering the boiler off and on again after a few minutes. However it now appears to not work at all for heating or HW.

I've done a bit of preliminary digging and checked all connections to the hive and boiler PCB. When doing this I noticed a faint ticking sound from the boiler PCB. Not sure if it's unusual as I wouldn't have heard it with the covers on.

I did check with a multimeter and can detect no voltage with respect to neutral on either of the 'RT' terminals on the boiler PCB.

If I put it into 'chimney sweep' mode, the boiler fires up instantly and I get heating/hot water depending on the setting of the hive.

Any pointers as to where I should be looking next? Boiler is just outside of warranty and unfortunately has not had annual servicing either so I think any help from Vaillant is unlikely.

Thanks!
Ted
 
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I did check with a multimeter and can detect no voltage with respect to neutral on either of the 'RT' terminals on the boiler PCB.
Not really sure what you mean by that ?
the hive doesnt send power to the boiler to come on, the hive powers the zone valves and in turn the valves send power to the boiler to come on, are the valves opening when selected ?
 
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where I should be looking next?
Wiring centre where the valves are connected.
Possible failures are the switched output to the boiler being disconnected, or the 230V input to the valve switch is disconnected, or the microswitch has failed in both valves.
Boiler is unrelated.
 

CBW

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If you’re getting heating or hot water in chimney sweep mode, I’d say the zone valves aren’t making their microswitches and sending a switch live to the boiler.
 
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Thanks for the replies, with your help I've managed to isolate the problem. As you say, looks like I was barking up the wrong tree with the boiler. Have done some reading up on how S plan works and it makes total sense now.

The 2 port valve for the heating seems to be the culprit - I did some checking with the multimeter and when it's energised, the microswitch isn't passing the 240v through to the boiler. I took the cover off the (Honeywell) valve and gave the motor a sharp tap. The lever moved a few mm accompanied by some ticking noises and the boiler fired up.

Now I think about it, a few weeks ago I noticed that here would be an odd pinging noise a few seconds before the heating fired up - almost like someone twanging a spring 4 or 5 times and it reverberating around the heating pipes/radiators. This noise did go away though but I have also noticed some 'odd' sounds before the heating fired up since then.

None of that expalins why the hot water wasn't firing up either though, although until I see otherwise I'll put that down to operator error and assume the water was already hot!

Cheers for the advice guys, looks like I'll be needing to replace the head of the valve. The valve is probably under 3 years old as it was installed when the unvented cylinder was installed and the system converted from Y plan to S plan.

Thanks,
Ted
 

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