Overheat that won't clear - Baxi Solo3 with 2 heat 1 water

[zummertor]

Hi, wonder if anyone can help, I have an overheat on a Baxi Solo 3 PFL60 that won't clear.
The system has two heating circuits (upstairs and down) and one hot water.
This will probably be self caused but I seem unable to clear the problem.
Due to building work one of the rads needed changing to a larger one, having done this successfully on the upstairs circuit I followed the same process for down.
As the pipework needed extending a short distance I opened Honeywell silver valves by moving small latch to side and catching them.
Drained down the pipework, extended new pipe for new rad and fitted rad.
Re-filled system back to pressure releasing air from rads both up and down.
All hot/cold taps opened and run to ensure no splurting of air.
Ran hot water only which then tripped to overheat within minutes. After a while it would reset, tried downstairs heating circuit but nearly straight to overheat and wouldn't reset.
I had a look at boiler and to top right hand side is a pipe with a valve similar to a rad on top, I opened this and let air out.
Still could not reset boiler from overheat.
Water pressure in system is between 1 and 2 as per normal.
Red lock valves are open(screwed out).
I've read quite a lot of posts but haven't found something similar to this other than several overheat type issues.

Any advice on where I've gone wrong and what I should do to fix the problem ?

 

[weareleeds]

You probably have a problem with air hence no circulation causing overheat. It should reset when boiler cools down again but if there is no water movement it will overheat again. Are there any bleed caps anywhere to release the air & have you bled the pump

 

[zummertor]

Thanks for the fast reply.

I have turned screw on top of pump and water dripped out immediately so I shut it. I'm guessing that is the way to do it.
I noticed the pump casing is very hot when I did that.
I'm not sure what I'm looking for when looking for a bleed cap, are there any pictures to help me in my hunt ?

 

[zummertor]

I think you are right, it did eventually cool down and I reran it again and heard a lot of air movement, stopped it and re-bled boiler and got more air out.
It seems to be running OK now on hot water only, but I'll go back and check again in 30 mins to see if any more air has circulated.

This is a super forum made by the people posting their expert knowledge.
Thanks.

 

[ChrisR]

Here's this one n case you didn't come across it...
Vent at V

 

[zummertor]

Thank you ChrisR.
There are three drainage valves where you can attach a hose so do / could those serve a dual purpose ?
System seems to be stable now for couple of days so probably was air lock.
The one thing I forgot to check is the second boiler which is in a different room and is normally shut off and it had air in it as well.
I have no idea why 2 boilers but it appears they can either operate separately or together, and are of different ages so maybe when an extension was done they added a second rather than replace with a bigger one.

Are there any diagrams around of how these might be configured in theory, I'll have to sketch out where all the pipes and electrics run but would like to know the theory so I can understand what is going on.