38CDI: doesn't fire on heat demand, and Grundfos UPM3 stuck

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MrBalham

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The cold snap made me switch heating on for first time in 6 months which has caused 2 unrelated problems on a well maintained Worcester Bosch 38CDI. Grateful for any advice on:

1) boiler doesn't respond to Nest thermostat 1's call for heat, either wirelessly or on manual override next to the boiler. Have reset the Nest and the boiler but problem still persists. (Pic 1 - manual Nest override looks like it's calling for heat but 38cdi not firing)

2 but it responds to Nest 2's demand showing boiler is functioning, but the Grundfos UPM3 shows an error and won't restart even when using the anti-clockwise unblocking procedure with the screwdriver (Pics 2 and 3, UPM3 quickly defaults to error mode)
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Any ideas about either please?
 
MrBalham said:
1) boiler doesn't respond to Nest thermostat 1's call for heat, either wirelessly or on manual override next to the boiler. Have reset the Nest and the boiler but problem still persists. (Pic 1 - manual Nest override looks like it's calling for heat but 38cdi not firing)
Click to expand...
If you link-out the call to heat and the common (terminals 2 & 3), within the Heatlink, and the boiler fires - that could prove that the Heatlink is dead.
If you aren't sure how to to that, post a pic of the wiring within the Heatlink, and we should be able to help.
 
Thank you for your reply.

The Heatlink has an earth, brown and black coming into the junction block. I've looked at the Nest instructions but can't tell what should happen to these wires afterwards and how they should be linked to the zone valves and incoming 240v supply, so any advice would be very welcome.

And how I can jump them to simulate a call for heat.
IMG_7293.jpg
 
1) there is a grey wire I missed, coming out of the Heatlink into the junction box

2) here's the open Heatlink
IMG_7294.JPG
 
MrBalham said:
1) there is a grey wire I missed, coming out of the Heatlink into the junction box

2) here's the open Heatlink View attachment 317470
Click to expand...
It's probably easier to do in the Heatlink - with the power off, just place the grey and yellow/green wires into the same terminal (2, or 3, it doesn't matter).
If the heating comes on when the system is powered back, the heatlink is likely to be faulty.
If the boiler still doesn't fire, the problem is elsewhere.
 
Good news: I jumped the grey and yellow/green in the Heatlink and the boiler fired. It also seems to have "unstuck" whatever electronic glitch had been happening and Nest 1 is now controlling the boiler again.

Bad news: the Grundfos is still stuck and short of swapping it out, I'm not sure what I can do with that..
 
Harry Bloomfield said:
Did you definitely engage the screwdriver in the slot in the end of the shaft, spin the shaft, and feel it turn?
Click to expand...
Yes I can feel it engage, and depress the spring to engage. It doesn't want to turn anti clockwise and it feels like it's jumping out of the head so I don't want to continue and risk stripping it.

I've looked for videos to see if you can remove just the black "electronics" back part of the pump so I can get to the screw reliably. But there doesn't seem to be a way of doing this.
 
It looks as if you may have isolation valves at each side of the pump, so you can take it out for further investigation. Might it be choked with sludge, or perhaps some debris??
 
Last question - the Grundfos doesn't look like it will come out as there is no give in the horizontal pipes on the manifold. Any suggestions about the best way to remove it please?
IMG_7302.JPG

I could end up dismantling everything!
 
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