Not sure why you’re opening the boiler up, but I wouldn’t have thought that’s normal. Stop using the boiler immediately and seek a gas safe registered engineer to take a look. It could be one of the known failure logics.
The glow calmed down. I think what I did is tried to top up the boiler and open the two valves on the fill loop to raise the pressure but I closed the return and flow valves also so the pump was constantly running hot as the tado thermostat was staying on as no water was moving around.
I’ll get someone to replace the spark electrode as the heat transfer plate has a crack and is missing a bit.
Yes it's something to be concerned about - shut it off and don't use it till a GSR engineer can get in to fix it, service it and test it. That's unsafe.
As suggested that isn't DIY territory as it's a room sealed case.
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