Faulty brand new Viessman boiler - help! (PigletJohn?)

[Worried345]

A few weeks ago, our central heater boiler broke down and we've had no heat since. I found what I thought were a good local company to fit a really good boiler - a Viessman. They're on day 3 of works today (costing almost £5,000 and I've already paid 60% of this!!!).

The boiler won't fire up and stay fired up and is indicating a Fault C on the panel. It initially was OK for about 30 mins the boiler company have said but then stopped working. They are now hoping that a Viessman engineer can come out soon tomorrow, although the boiler man here is supposed to be Viessman registered himself.

In the meantime, we have a v expensive but faulty boiler. The boiler man thinks it's a faulty programming panel. Does anyone have a clue if this might be the case and if Viessman boilers tend to fail initially? Is there anything obvious which the boiler man here might not have thought of?

He's fitted new gas pipes, a new 'plume/flume' thing and new pump. All rads. were released of air etc.

I'm pretty desperate as I timed my work and other stuff around the works being completed tomorrow and have to be back at work from Saturday. Juggling DCs on hols too and had also arranged some halfdays next week to give them various trips out/celebrations for DS1s birthday. They've been in the house in front of PCs all week (still too young to go out alone), whilst I've been looking after the workmen and making them cups of tea, clearing up after them, wiping up water etc etc.

PigletJohn - you were extremely helpful when the boiler first broke down on my original thread. Any ideas what a Fault C fault means and how 'cureable' it might be?? Many thanks to anyone who may be able to help or offer hope.