warmflow utility combi 70 HE diagnosis help needed

hi guys,

boiler initially had lockout  and low pressure lights on so i drained system down by removing flexi from expansion vessel and then refilled via filling loop and went round bleeding all the rads.

pressure guage was rising ok so i believe the low pressure switch to be at fault. bypassed this temporarily by reversing switch cospnnectors and boiler fired up fine. rads warmed up nicely but after 20 mins burner stopped leaving pumps running as i believe they should. after that the burner wouldnt start when theres a call for hot water or c/h unless boiler is powered off for a while and powered on. 

i realise i will have to replace the low pressure switch and that its not a good idea to leave it bypassed as its there for a good reason. 

any ideas guys? 

If the temp of the Return is close to the temp of the Flow, the boiler won't fire up. Could that have been the issue?

condensate pipework blocked or frozen?

Try and find the install instructions and take a look at the fault finding section. is this it http://assets.grahamplumbersmerchant.co.uk/product-docs/16862/16862.pdf

Remember to add some inhibitor if you have drained down.