Combi-boiler on internal wall

We have an Ideal logic combi 35 boiler fitted to an external wall. For cost reasons we are looking to deviate from the approved extension plans we already have approved & a couple of builders say the boiler can remain in place as it already has a flu extension going up the current external wall.
The proposed works will mean this 'external wall will become an inner wall and the flue will project through the ceiling/roof.
i'm fine with all that but I thought this boiler draws in air at the point it comes out the wall, therefore it needs to be on an external wall, or is there a flue that caters for this.
Forgot to say 2 builders say this is ok, one of them has a gas-fitter working for him whilst another guy says we'll need a different boiler

Where the flue terminates at the minute (outside) you could replace the terminal with an extension, elbow up through ceiling with a vertical terminal. This is fine but remember to get flue inspection hatches fitted so the whole flue can be visually inspected. Turned a few boilers off recently through exactly the same scenario. P.S. Don't trust the builder who says you need a new boiler

Where the flue terminates at the minute (outside) you could replace the terminal with an extension, elbow up through ceiling with a vertical terminal. This is fine but remember to get flue inspection hatches fitted so the whole flue can be visually inspected. Turned a few boilers off recently through exactly the same scenario. P.S. Don't trust the builder who says you need a new boiler

More than that don't trust anyone who is not gas registered and certainly NOT builders who usually have little understanding of gas boiler safety.

Better too to ensure you have a contractual relationship with the person giving you advice.

They then become legally responsible for the advice they give you.

Tony

I know to my cost not to trust builders.
The boiler is new, fitted last year under the 'free' nest scheme so any work shall probably need to be carried out by British Gas anyway,

No any gas registered engineer can do modifications to the flue.

At least that is the case unless its prohibited under special "Nest" provisions.

The only "Nest" that I know is the wifi programmable thermostat which I can install!

Tony