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Vented system to Combi

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TotalR

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Hi,

So I can get my head around the work involved in this. currently have vented system with boiler in kitchen. Moving to Combi, staying in kitchen. has 22mm gas suuply and condense pipe can go straight out the wall. Hot & cold already in cupboard.

in the airing cupbaord what needs to be done to the Feed & Return here? system is as below but with 2 valves one for heating one for HW.

upload_2019-4-30_15-22-57.png
 
Can't you discuss this with your installer? I'm sure you can understand why we would be reluctant to give out advice on a boiler install to non gas registered forum users.
 
I could yes. However I want to know now, hence my question and the point of a forumn? I'm not asking anything to do with the boiler (gas). Is the airing cupboard pipe adjustments as per below.
 
Last edited:
Personally I would seek advice from a few different plumbers, combi boilers may often be cheaper but they come with quite a few drawbacks including:

The on demand nature of the hot water means unless you fit quite a large heat output one you may struggle to run a shower while someone is washing up for example.

Another consideration in loosing your HW cylinder is you are solely dependent on your boiler for HW as you no longer have an immersion heater for emergency use.

Adding renewable heat sources is more complex/limited should you choose to in the next 10-15 years.

Combi boilers are more complex that system boilers, in theory at least the less there is the longer life you're likely to get from it.

Just my 2p/opinion, but I'd always suggest a customer asks for the drawbacks of any system as well as the positives.
 
OffshoreGas said:
Personally I would seek advice from a few different plumbers, combi boilers may often be cheaper but they come with quite a few drawbacks including:

The on demand nature of the hot water means unless you fit quite a large heat output one you may struggle to run a shower while someone is washing up for example.

Another consideration in loosing your HW cylinder is you are solely dependent on your boiler for HW as you no longer have an immersion heater for emergency use.

Adding renewable heat sources is more complex/limited should you choose to in the next 10-15 years.

Combi boilers are more complex that system boilers, in theory at least the less there is the longer life you're likely to get from it.

Just my 2p/opinion, but I'd always suggest a customer asks for the drawbacks of any system as well as the positives.
Click to expand...

Thanks appreciate the advice. I have taken all into account, and a 35-40kw chucks out enough water for us. We have good mains pressure also. Given a Combi is around 1500 fitted with 7 years warranty I’m happy it’ll pay for itself as the winter gas bills were extortionate on current set up. I initially was thinking of keeping the system because of said points, however most recent plumber asdvised bigger Combi would be fine.
 
scott_d said:
Which boiler are you getting for 1500 fitted?
Sounds very cheap

I got got a price for a Vaillant boiler, flue, filter and controls and it was more than 1500
Click to expand...
Baxi 636 I’m looking at. May go down the more expensive route of a worcester/Vaillant but can’t see any reason too right now.

Any responses on my initial question?
 
TotalR said:
Baxi 636 I’m looking at. May go down the more expensive route of a worcester/Vaillant but can’t see any reason too right now.

Any responses on my initial question?
Click to expand...

HW obviously comes directly from the boiler and not your tank. You installer will need to make a connection between your existing HW pipework and the new boiler. This may not be ideal as your existing pipework should be deigned to suit the location of your existing tank.

I'd also question where your plumber intends to cap off the HW pipework to your cylinder as dead legs (especially containing wamr water) pose a risk of Legionella.
 
OffshoreGas said:
HW obviously comes directly from the boiler and not your tank. You installer will need to make a connection between your existing HW pipework and the new boiler. This may not be ideal as your existing pipework should be deigned to suit the location of your existing tank.

I'd also question where your plumber intends to cap off the HW pipework to your cylinder as dead legs (especially containing wamr water) pose a risk of Legionella.
Click to expand...
Hot water will be connected in the cupboard of the boiler as current hot water to kitchen tap runs through there. Not sure on the dead legs as two bathrooms are either side of the airing cupboard so hopefully not a big run.
 
You won’t get any advice on unvented cylinder plumbing as you need to be G3 qualified to work on and install unvented cylinders
 
Personally I feel replacing a low pressure system to a combi the pipework has already stood the test of time and it is time to fully replace all system pipework! Been to countless installs where there are leaks due to system pressure change.
 
Cold into the boiler
Hot water out

Heating flow from boiler to radiators
Heating return from radiators to boiler

Don’t forget the heating filter, flush, chemicals, lime fighter, shock arrestor, additional expansion and boiler plus controls.
 
sammathias said:
Personally I feel replacing a low pressure system to a combi the pipework has already stood the test of time and it is time to fully replace all system pipework! Been to countless installs where there are leaks due to system pressure change.
Click to expand...

Wise words, quickest way to find a weakness in a system that’s been operating barely above atmospheric pressure for 20 years is to shove 1.5 bar in it.
 
TotalR said:
20plus year old non condensing inefficient boiler with old copper cylinder. Was going to upgrade to unvented and new system boiler but big Combi cheaper and more convenient.
Click to expand...
Quite honestly you are probably
much better keeping your existing set up
most modern boilers are all rubbish and the combis even worse, loads of people make loads of money specifying, selling and fitting in reality pathetic units, that will not last
7 years or even less.
That is my opinion ..been in this game many years in all sorts of roles ...Rob Foster
aka centralheatking
 
sammathias said:
Personally I feel replacing a low pressure system to a combi the pipework has already stood the test of time and it is time to fully replace all system pipework! Been to countless installs where there are leaks due to system pressure change.
Click to expand...

Had the pipe work replaced recently, was all 8mm micro-bore when I moved in. System has a pump on it at the moment anyway.
 
Rob Foster said:
Quite honestly you are probably
much better keeping your existing set up
most modern boilers are all rubbish and the combis even worse, loads of people make loads of money specifying, selling and fitting in reality pathetic units, that will not last
7 years or even less.
That is my opinion ..been in this game many years in all sorts of roles ...Rob Foster
aka centralheatking
Click to expand...
Just a toss up atm between a very expensive Baxi Solo which works with niggles, or upgrade to Combi.
 
TotalR said:
Thanks appreciate the advice. I have taken all into account, and a 35-40kw chucks out enough water for us. We have good mains pressure also. Given a Combi is around 1500 fitted with 7 years warranty I’m happy it’ll pay for itself as the winter gas bills were extortionate on current set up. I initially was thinking of keeping the system because of said points, however most recent plumber asdvised bigger Combi would be fine.
Click to expand...

Combi conversion for £1500!!! Wow
 
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