Truma heating issue

Hello,
Hoping to get some help please,
Our Truma Combi is not heating on gas
We were staying in a pub car park recently with no hook up, we could not get the heating to come on with gas only,
It came on with the yellow light, but then it went on to a constant red light, the fridge and oven were ok on gas,
Tried it today, on our drive, on electric only it is working,  then I tried mixed elec and gas.. red fail light came on,
Tried again with gas only, failed again.
Is there something I am not doing? Not very clued up I'm afraid,
The controls are manual 2 small dials, one to select supply heating method, the other to select what you need to heat.
We have a Nuevo 2012.
PS got plenty of gas
Many Thanks for reading
Kriss x

Experienced a similar issue and discovered that I hadn't removed the external venting cover. Once I did that, all was good as a safety measure, it doesn't ignite while that cover is on.

Is tap for the heater turned on at the manifold?

Thanks MalMonty, we tried taking the heater cover off, didnt solve the issue unfortunately

Thanks Paul, 
Hubby said he's checked, but just incase, where should I look please?
Kriss

taffykriss wrote:Thanks Paul, 
Hubby said he's checked, but just incase, where should I look please?
Kriss

Look under sink or a side bench, you should find a set of 3 or 4 red taps marked on their ends with symbol of fridge, cooker and heater.

Ah, i think ive seen them!, Thanks Paul, very helpful, will take alook tomorrow 
Thanks again
Kriss