Thermecon oil boiler issues

[botty99]

Hello All. I wonder if anyone can help.
My boiler decided to stop working on me.
It's a thermecon oil system boiler.
The circulation pump gave up the ghost so I replaced it.
Now, if I run just the hot water the boiler overheat stat trips out on me after a few minutes.
If I run the heating it's all ok.
I've bled the air from the rads.
Any ideas?

Thank you.

 

[Boilerman2]

To the right hand side of the pump is a grey plastic knob, this is a manual air vent unscrew this a few turns until it hisses and then water will come out (careful as it will be very hot! turn off once water flows freely all should then be OK

 

[botty99]

Thank you for that Boilerman.
I did actually do that earlier but it still seems to be overheating.