Janus 3/30 Water Boiler - Flue question

[DaveM543]

We have a Janus 3/30 water boiler which is currently flues through an asbestos flue jointly with our warm air boiler. There is damage at the ridge terminal and so we are considering its complete removal of said flue. Ignoring the warm air boiler as plan to replace. The janus document says the flue should be 75mm (3in) as standard, with adapter plate to convert to 100mm (4in) flue.
1. Does this mean a 5in twin walled flue as I have not seen 4in
2. Does flue work have to be done by Gassafe, or Hetas or can any competent builder do the work?
Thanks

 

[gas112]

Why go to all the expense of removing and replacing the existing flue when all it will need by sounds of it is a new ridge tile and R type adaptor.
New flue will cost you several hundred quid

 

[DaveM543]

The gas engineer tells me that as well as replacing damaged ridge terminal we HAVE TO also replace the 3 metre plus 2 bends section of asbestos flue from where it enters the attic near eaves up to the ridge with twin skin
He says there is an adapter to connect the twin skin to the asbestos pipe as it enters the attic

 

[gas112]

Twin wall is better but it is acceptable just to repair the damaged bit if the flue was being renewed then it would definitly have to be in twin wall.

Single wall in a loft should be wrapped with fibre glass or some other form of insulation
If i was replacing with twin wall i would just take it through the tiles as a lead slate is cheaper then a new tile and adaptor and prob easier to position.

 

[simond]

If you are replacing the wau, just get a combi. This way, you get a water heater pretty much for free.

Paying someone to get up on your roof to put a flue in is an expensive business.

If you are staying with warm air, consider a Lennox condensing unit, they are 94.5% efficient.....