Hive wired incorrectly to Baxi Solo 2?

[Richard M.]

Hi all

Puzzling one which my local heating engineer can't solve, who gave the boiler a clean bill of health but doesn't know much about Hive.

I'm obviously not an engineer but I'm convinced the Hive wiring is at fault here somehow. The system was installed before we moved in. I found a similar thread on the forum here detailing the same issues but the wiring on that boiler was different.

The Hive will start the boiler no problem. The boiler works beautifully at this point. The problem starts when the Hive shuts the boiler down. When it does, all the lights on the boiler deactivate. At this point one of two things happen;

Result 1: If the boiler wasn't firing up at the time the Hive shuts it down, ie. the boiler's own thermostat had powered it down, all is well and calm.

Result 2: If the boiler was at full chat when the Hive shuts it down all hell breaks loose. Banging, clanging, world-about-to-end type stuff, followed by the overheat light coming on. Wait five minutes for things to cool down then reset and the boiler works fine again.

You can see a video of result 2 in action HERE.

I've attached a pic of the wiring into the PCB.

I've tried the boiler thermostat in all sorts of different positions all the way down to 1.5. The PCB is brand new but the boiler did the same with the old PCB.

Any ideas?

Thanks in advance.

Richard

 

[cross thread]

Sounds like no permanent live to the boiler

 

[stem]

The Hive is just a simple on/off switch that's all it does, nothing more, so it its switching on & off as per the room thermostats setting, it's doing all that it should. The fault will be elsewhere.

When the Solo 2 goes off, the pump should continue to run and circulate water around the system. This is because there will be residual heat in the boiler that must be got rid of. If this doesn't happen the boiler will 'kettle' (ie boil the water inside it) and make the sounds you are hearing, and the overheat light come on. I suspect that either the system doesn't have a satisfactory by-pass to allow the water to circulate sufficiently when the boiler goes off. Either because it's been incorrectly installed, the regulator valve on the by-pass is incorrectly set, or the pump isn't continuing to run after the boiler goes off. This could because the boiler isn't telling it to, or the pump isn't wired to the boiler correctly.

EDIT:
@cross thread has a point. The permanent live is what provides power to the pump to keep it running when the boiler goes off. In your case, there is a wire connected to the permanent live, a check with a multimeter will check whether it actually is live or not and if it is permanent. This is the wire in question.

And the wire highlighted below should be connected to the pump, and continue to be live for about 5 to 8 minutes after the boiler goes off.

I don't know why your heating engineer can't sort it, it shouldn't be difficult if they are present when the fault occurs. The problem is that the residual heat isn't being got rid of when the boiler goes off, they just have to find out why not.

 

[picasso]

Live and switched live probably the wrong way round.

 

[stem]

It could even be a plumbing issue. I once came across a boiler with the exact same symptoms. It had been converted from a Y-Plan [3-Port motorised valve where at least one port was always open] to an S-Plan [2 x 2-Port motorised valves that closed completely] when both valves closed, there was nowhere for the water to flow and so it overheated.

 

[Richard M.]

Really appreciate all the advice everyone, thank you. I'll work my way through the different ideas and fingers crossed one of them works. Will keep you posted.

 

[Richard M.]

Ok, I think we're there. Thanks to all. I troubleshooted as follows:

Checked the PCB was wired correctly using a multimeter as suggested by @cross thread , @stem & @picasso . All good there, Hive is fine and working as it should, so boiler / plumbing issue. The pump is also running after shutdown so that's also wired correctly too.

@stem 's comment got me thinking though - why wasn't the water circulating sufficiently? I looked at the bypass valve first and raised it up by two marks (see pic). This nearly solved it - the noises were less frightening and infrequent compared to where it was previously, but the boiler was still overheating. The valve was pretty much at maximum (minimum?) setting now so my only other option was to increase the pump's flow rate so I set it to maximum (see pic). This did the trick and everything works fine. Phew.

If there's any thoughts on these settings please let me know. I could try putting the valve in its original setting and leave the pump at its current setting and see what happens, but everything is working now and I'm a firm believer if it ain't broke don't fix it!

Thanks again everyone.

Richard

 

[stem]

Puzzling one which my local heating engineer can't solve,

Time to find a new one methinks, rather basic fault finding really. But well done you.

 

[ericmark]

I was told by my heating engineer could not fit a motorised valve to DHW for same reason, it cools by getting rid of excess heat into the DHW. My boiler is oil with no run on.

 

[Richard M.]

Time to find a new one methinks, rather basic fault finding really. But well done you.

Would you believe I've had FOUR heating engineers try to solve this? This forum was my last resort. First two were emergency engineers from my Home Emergency policy - one telling me I needed a new boiler and they could provide a quote, the second one saying there was a blockage in the plumbing and it would be a big job to find it, the third one actually playing around with the bypass valve and it worked whilst he was there so left but obviously it came back (same day) and the last one also played with the bypass valve but couldn't solve it. Not one checked the wiring and not one changed the pump setting.

So thanks again for pointing me in the right direction. I'm quite sure you've saved me several thousand pounds.