Potterton Suprima with megaflow unvented cylinder issue

[smmjh11]

I have a Potterton Suprima boiler which connects to the Megaflow. Today it started to have an issue as the boiler keeps shutting off and needs resetting. It seems that water is not flowing round the primary flow and return. The pipes are really hot at the top of the boiler so I assume that there is no flow round the system which is causing the boiler to overheat and trip out.
The pressure on my external expansion vessel is fine and I there are no leaks. Am I too assume that the pump could be faulty as it seems more noisy than usual as there is no flow around the primary circuit ( I thought that maybe even if the pump was faulty the hot water would still work its way around, but maybe not.
Can you get airlocks on pressurised systems.
Thanks

 

[oldbutnotdead]

Pump does sound possible, could be motorised valve failure, could be frozen pipes (unlikely now), could be a big fat airlock (is the primary circuit open vent or pressurised)
Does your pump have a big shiny slotted cover over the centre of the impeller - if yes then undo it (have some rags handy, you'll get a bit of water out), fire up the boiler and see if it spins.

 

[smmjh11]

Hi Old, I took the centre screw out of the pump and little bit of dirty water came out. I then turned the boiler on and the centre bit spun round and a little bit of water came out. Had a tray underneath which captured any water but did not need any towels. I believe I have a pressurised system as I have an orange external Zilmet expansion vessel just above the Megaflow cylinder. Also I have taken the cover off of the 2 port motorised valve so it should be open but no heating comes through.

 

[oldbutnotdead]

Does the valve have a manual lever on it anywhere? If yes, try it- there should be resistance but it should move. Does the pipe into the valve feel hotter than the pipe out (try about a foot either side of the valve)

 

[smmjh11]

I think it must have been an air lock as it has started to work. Taking that centre screw completely out and turning it on must have solved the issue.

Thank you Oldbutnotdead

 

[oldbutnotdead]

Happy days!