baxi duo tec combi e133 error code?

Gas Networks have recently replaced all the gas pipe in our road which made it necessary for them to turn off gas for a day. Baxi boiler duo tec combi 33 is 18 months old and worked perfectly until gas works. Re- lit by gas technician and since then have had error code e133 about 3 times a day. It seems to fail every time we ask for heating and hot water. Resets with no problem. Any suggestions?

Katieaitch
February 2011