Viessmann Boiler Flexible Flue System

[ROB81E]

Hi.

Does anyone ere have any experience of fitting flexible flues?
I currently have an ancient floor standing open flue Potterton boiler which needs upgrading due to new extension. This currently flues through existing chimney structure.
We would ideally like to keep the boiler in the same location, which is in centre of house with no easy access to external wall.
Various engineers have stated that it is not allowed to flue up through existing shaft, though I understand Veismmann do a flexible flue system which may be suitable
We were looking at possibly installing a thermal store or large combi. Unvented is not an option as we have no option for discharge without this being pumped.
We have 190m2 of UFH and 8 upstairs Rads and 3 bathrooms.
Would value any advice please.
Cheers

 

[muggles]

Never fitted the Veissmann flue liner but I have done the Intergas one which worked well. I really wouldn't recommend a combi for 3 bathrooms, you'd be much better off with separate storage. Also be aware that most combi boilers (Intergas excepted) need a pressurised system to operate, and so have a pressure relief valve which needs to discharge somewhere. Storage combi's will have two pressure relief valves. Thermal stores are terrible for condensing boiler efficiency, they run too hot. Are you sure there's nowhere an unvented cylinder could be fitted? The loft maybe?

 

[ROB81E]

Loft isn’t suitable for a cylinder as it’s dormer so very limited headroom. Utility room has the space to house a cylinder and ideally we would keep everything there.
Is it not an option for condensate pump to be utilized with Combi?
Flow to house is about 22lpm and it’s extremely doubtful that 3 showers will ever be running at the same time.
When you say thermal stores are terrible as running too hot, do you mean that store doesn’t absorb enough heat from boiler flow?

 

[muggles]

Yes, a condensate pump can be used for a combi, and some combi boilers permit both condensate and pressure relief to discharge into the same outlet. The condensate pump would of course need to be suitably rated for the job.

The difference comes when you get to storage combi boilers, which are usually covered by the same regulations for temperature and pressure relief as unvented cylinders. Ergo if you can't have an unvented, you can't have a storage combi either.

Condensing boilers only start to condense when the flow temperature is below 70°C and the return is below 50. Full condensing occurs at 50/30, which is the temperature their efficiencies are rated at. Thermal stores need flow temperatures of 80-90°C to operate correctly for hot water, way out of condensing range which means your new boiler will revert to standard efficiency of around 80%

 

[ROB81E]

So looks like Combi with flexi flue may be only realistic option. Are intergas Combi’s highly rated by you guys and gals? and do they do one with large enough flow rate at all?

 

[boringoldcodger]

A while back there was this thread about which boilers the pro's on here had at home:
https://www.diynot.com/diy/threads/...nd-of-boiler-do-you-have-in-your-home.565931/

 

[JohnD]

So looks like Combi with flexi flue may be only realistic option.

No it isn't.

We would ideally like to keep the boiler in the same location

Reconsider.

 

[Gasguru]

3 bathrooms and a substantial house by the sounds of it....your priorities are all wrong...re-configure and make room for a cylinder and boiler.

 

[vulcancontinental]

There are many boilers, system and combi that can use a flexible flue, Viessmann, Intergas, Baxi, Vokera, Atag etc. Sealed system PRV into a Grunfos conlift pump. Hot water remains the same as existing. 3 Bathrooms too much for a combi.

 

[ROB81E]

Hot system staying the same not really an option and no other location is as preferential for boiler. Gas and water are in this location. It’s a big decision as you all know and we want to make the best choice possible in the circumstances.
there hasn’t been a general consensus on the best way forward from anyone that’s seen it yet. 3 installers have stated that flexible flues are not allowed, point blank and I can understand why it wouldn’t be the preferred option for installation but at least we know it is possible and can factor it in.

 

[sxturbo]

You could go for a high efficiency combi boiler with good hot water flow, like the intergas xclusive with flexible flue kit (https://theintergasshop.co.uk/intergas-flexible-flue-system/1109-intergas-flexible-flue-kit.html) and install a salamander pumped accumulator to provide you with consistent water pressure.

Installing the accumulator keeps consistent water pressure regardless of how many taps are opened when demanding hot water. It also removes the pressure drop when a cold tap is switched on (common issue with combi boilers) whilst in the shower which is rather irritating when it happens.

 

[muggles]

So looks like Combi with flexi flue may be only realistic option. Are intergas Combi’s highly rated by you guys and gals? and do they do one with large enough flow rate at all?

Yes, Intergas are great boilers. Their biggest combi is a 36kW though, which won't do the 22l/min you want. Might well be better off replacing with another regular boiler supplying your existing hot water cylinder?

 

[bernardgreen]

Installing the accumulator keeps consistent water pressure

How long can the accumulator keep the pressure constant ? It does have a limited capacity.

 

[bernardgreen]

Might well be better off replacing with another regular boiler supplying your existing hot water cylinder?

Sensible advice

 

[dilalio]

Sensible advice

So, can you now see Bernard that installers don't just push a combi on a customer?
Remember the first rule of business... The customer is always right... Even when they're wrong!