Potterton E1 33 fault?

i have a Potterton Promax Combi He plus. The E1 33 fault keeps showing. We have had the ignitor changed, Calor gas have changed the regulator on the gas tank, it showed 42mb and should have been 37mb. the boiler works for several days after someone has had a look at it then stops working and E1 33 shows.
Ive done the hot kettle on the white pipe...but it is not cold enough to be frozen so i doubt this is the problem.
Currently running out of ideas....boiler man is coming out this afternoon to have another look....
Anyone any ideas on what can be done? 12month old baby enjoys a hot bath and a warm house!!!!