How much work to change from conventional boilet to combi boiler

[kitcat123]

Hi All,

Was wondering what work would be required to change from a conventional boiler setup (hot water cylinder) to a combi boiler?

Would new pipework be required?

Thanks

 

[JohnD]

How many people live in your house, and how many bathrooms/showers/WCs are there?

 

[CBW]

If you’re just changing the boiler, the only new pipes would be to get a cold feed to it, a hot outlet to join existing, and probably a gas pipe upgrade. It’s known as a conversion in the industry. Can I ask why you’re considering a combi boiler? Have you considered if it’ll cope with demands? Eg, how many hot outlets could be run simultaneously? Do you have sufficient water pressure and flow rates?

 

[roguetrader]

If you buy a ball of string from the pound shop, unwind it all and then measure it, you might get an answer.

 

[kitcat123]

How many people live in your house, and how many bathrooms/showers/WCs are there?

4 people, one bathroom and shower and one WC

 

[kitcat123]

If you’re just changing the boiler, the only new pipes would be to get a cold feed to it, a hot outlet to join existing, and probably a gas pipe upgrade. It’s known as a conversion in the industry. Can I ask why you’re considering a combi boiler? Have you considered if it’ll cope with demands? Eg, how many hot outlets could be run simultaneously? Do you have sufficient water pressure and flow rates?

Just a two floor three bed house with one bathroom and one WC. 7 radiators in total. Would like to go combi as the cylinder is a little dodgy, expecting combi boiler to use less energy and would like to get the space freed up from removing the cylinder.

 

[JohnD]

4 people, one bathroom and shower and one WC

With only one bathroom, a combi will work OK. It will be somewhat slow to fill a bath.

A modern boiler is more efficient than an old boiler, but combis are not more efficient than new system or regular boilers. There is delay and wastage as it fires up each time you turn a hot tap on.

If you have a cylinder, you can still have hot water when the boiler breaks down. When a combi breaks down, it is more of a calamity.

 

[Harry Bloomfield]

A modern boiler is more efficient than an old boiler, but combis are not more efficient than system or regular boilers.

Correct, and often overlooked. The reverse could in fact be true, depending on how/when you use hw, and you might be disappointed, by the rate of hw flow.

 

[CBW]

With only one bathroom, a combi will work OK. It will be somewhat slow to fill a bath.

Not necessarily, it all depends on pressure and flow rates.

What also need to be a factor a lot seem to forget is a combi will only heat the water on demand from the incoming cold main temperature, so colder water incoming in winter, which usually = less hot delivery than summer, when the incoming cold main is usually warmer.

 

[JohnD]

Not necessarily, it all depends on pressure and flow rates.

What also need to be a factor a lot seem to forget is a combi will only heat the water on demand from the incoming cold main temperature, so colder water incoming in winter, which usually = less hot delivery than summer, when the incoming cold main is usually warmer.

My bath fills at about 20lpm

Not much chance of getting a combi to do that

And as you say, will be worse in winter.

 

[Harry Bloomfield]

And as you say, will be worse in winter.

..and in winter, due to the cold being colder, less cold will need to be added to a bath, slowing the process even more..

With an open vented system, you can get full flow from both hot and cold simultaneously, so a bath fills much quicker.

 

[bernardgreen]

http://www.thnet.co.uk/thnet/BF/BFPages/overhist.htm is an old document but well worth reading.

 

[bernardgreen]

Without a hot water cylinder you will have no hot water when the boiler fails. With a hot water cylinder you have the option of using an immersion heater when the boiler has packed up.

 

[Fred Blogs]

Useless damn things. Anyone considering converting a traditional system to a combi system needs their bumps reading. They should be banned outright along with leylandias.

 

[denso13]

4 people, one bathroom and shower and one WC

I have an old, relatively small, combi in a large house and don't have any problems. Get what works best for you.