Which boiler do I need?

[Silverbirch]

Hi
Our gas central heating boiler is nearing the end of its life and I`m looking for some advice as to what type would be best to replace it with, conventional(if that`s the correct term) or combi.
At present we have a conventional boiler with 8 radiators in a three bedroom house with one bath and shower, which has served us well over the years. Apart from occasional visitors, there are usually just the two of us making demands on the hot water for showers and baths . I`ve had conflicting advice from a couple of plumbers I`ve spoken to regarding what would best suit our needs and reading up about it on the net still leaves me uncertain.
So, I`d be pleased to hear any advice from you chaps, whether you are an installers or just have experience of living with a combi boiler.

Thanks

Ian

 

[petermillard]

I`ve had conflicting advice from a couple of plumbers I`ve spoken to regarding what would best suit our needs and reading up about it on the net still leaves me uncertain...

Pretty sure you're going to get conflicting advice asking here as well . We've had a combi boiler for about 12 years without any issues at all. If your water pressure's ok (combi output can't be pumped) then a combi's a good choice; hot water on demand, no HWC taking up space, no heating a cylinder of water whether you need it or not, and conversely never running out of hot water.

Then again, no HWC means no airing cupboard (may not be a negative - more of a personal thing), the incoming water temp effects output i.e. colder incoming water in winter either takes longer to heat (pressure drop) or is just cooler generally, and because it's fed from mains pressure, the pressure does take a hit if someone runs a tap while you're in the shower.

Our condensing combi boiler feeds a 5 bed 2 bath house with 12 rads without any problems, just FYI. One oddity with a combi that my (elderly) parents had fitted last year - it came factory pre-set to deliver hot water at 55°C which is way too hot for them to run their hands under the tap, and there's apparently no way to reduce it which is a bit of a drag for them. I've offered to fit mixer taps for them but they don't want to go to any trouble, <sigh>

HTH Pete

 

[gregmcateer]

Pretty much as Pete says above.

One additional bit - if you have / may want ot have solar / air source / ground source water heating, you need conventional with a tank.

HTH

Greg

 

[defsdoor]

I have a Vaillant combi with a built in storage tank but it's probably overkill as the water pressure here is terrible. I think I need a new pipe from the house to the street. The amount of Limescale we get is shocking and I think the main water pipe is all clogged up with it. When we get the drive redone I might see how much it will cost to get the water board to put a new one in.

 

[nev]

One oddity with a combi that my (elderly) parents had fitted last year - it came factory pre-set to deliver hot water at 55°C which is way too hot for them to run their hands under the tap, and there's apparently no way to reduce it which is a bit of a drag for them. I've offered to fit mixer taps for them but they don't want to go to any trouble, <sigh>

HTH Pete

NOt all combis are like that, our Main combi has a temp control knob for both rad and water temps.

I cannot see any reason not to have a combi (unless as above you wish to add eco bits) but as said you need decent water pressure for sensible hot tap flow. (the heating side is sealed so once its pumped up its good to go). We are gravity fed from a tank so only have about 0.6 bar, which is not good for the HW flow - fine for filling a bowl but no good for a bath.

 

[Eric The Viking]

Pretty much as Pete says above.

One additional bit - if you have / may want ot have solar / air source / ground source water heating, you need conventional with a tank.

Spot on, in my opinion..

We have a 'system' boiler, a pressurised tank, and solar collectors on the roof. It works really well for us.

There are two significant disadvantages with combis: if you live in a hard water area, they can easily be damaged by limescale, and the hot water is slow to happen - filling a bath takes a very long time.

A pressurised tank is a sort of 'super combi' - loads of hot water on demand, and the boiler is almost as efficient as a normal combi. It needs no header tanks, either.

HTH,

E.

 

[mind_the_goat]

Most plumbers I've encountered are very conservative and tend to stick to what they know well, regardless of it being the best choice for the customer.
Combi will save on pipework but for a replacement that may be no advantage as you may have to remove a lot of existing pipes, and tanks. As mentioned you will loose the airing cupboard tank, if you have one, but modern tanks are so well insulated a new one may not provide much warmth anyway.
In my last house I went for a a Worcester Combi to save space and I was very happy with it. The sealed heating circuit also has some advantages in that once commissioned you shouldn't get air or other contaminants such as more lime-scale entering the system, I believe it's sightly more efficient too as there are no open pipes for heat to escape. You can of course get a sealed system on a conventional boiler. Modern hot tanks are very well insulated (repeating myself) and this probably makes efficiency savings with a combi harder to call. I guess if you use hot water in small amounts or at random times of the day, or want to save tank space, and have sufficient pressure then go for a combi. If you want an airing cupboard (make sure there is plenty of exposed hot pipe in the cupboard), use water at regular times and don't want to give the installer an easier job with less old pipe to remove (unless most of your old pipes are clagged up) then go conventional. Alternatively keep looking for a plumber who's advice you trust.
I'ts unusual to find a boiler with no water temperature control, but I guess it's worth checking before going ahead.
I brought my combi off the shelf, then struggled to find a plumber interested in the installation job, however the one I did find was good.
For my current house we replaced a conventional boiler with similar as it was easier.

 

[mind_the_goat]

if you live in a hard water area, they can easily be damaged by limescale

Good point, most manufacturer will claim this doesn't make much difference, but I did fit a decent water softener in that house. Something I'd also recommend in a hard water area and it's 'on the list' for current house.

 

[johnny]

I think with today's price of gas there surely is little argument for having a conventional boiler with hot water storage .?

We bought our current house 2x years ago which unfortunately had just had a new conventional CH & HW boiler fitted and even with being frugal with the heating and hot water our anual gas bill last year was £1250+ (tiny 3xbed cottage)
Unless you really cannot live without having frequent baths or perhaps have some disability in the family it really doesn't make sense to have a 25/30+ gallon HW Tank sitting in your airing cupboard all day and night with the boiler constantly heating it just to do washing up occasionally

Incidentally I believe the reason some boiler manufacturers set the minimum water temperature to 55degrees is to prevent Legionella bacteria from forming in the hot water pipes and fittings :wink:

 

[petermillard]

I'ts unusual to find a boiler with no water temperature control, but I guess it's worth checking before going ahead.

Yes, that's why I mentioned it as an oddity - my combi also has +/- control for rads and water, and I think my folks assumed they all do. Same make as mine as well - Worcester Bosch.

Good point about HW Cylinders being efficiently insulated these days, btw.

Cheers, Pete

 

[monkeybiter]

We have a Baxi with a small internal pre-heat tank suposedly for quicker HW to the tap.We can set temps on CH and the pre-heat, but not full flow HW. I'm a bit of a girly when it comes to hot things, so we have mixer taps.

 

[pebbles]

There's a very simple but new (last year) Ideal combi in the 2-bed/1 bath) house I'm in at the moment (Hull, where Ideal come from) ... only a bath (no shower) and it fills fast enough, set to 2 bars pressure, and there's an anti-calc thing fitted to the pipe and a furnox thingy too. I like it as it's mechanical rather than electronic - time clock on the front with pins, very obvious tap or rad symbols etc to choose settings. Me and idiot proof.

It wouldn't have been expensive... available as part of a local LA grant scheme for replacing ancient inefficient boilers - can't imagine them chucking the money around. Been trying to find pictures that resemble it online - no luck sorry...

 

[Silverbirch]

Pretty sure you're going to get conflicting advice asking here as well .

HTH Pete

Don`t worry, Pete, I`m not expecting a definitive answer.
The replies so far are helping me to clarify the pros and cons, which is what I`m after really.

Ian

 

[Eric The Viking]

Is the legionella thing because of new plastic pipes? Copper is poisonous to most bacteria, and so it can't happen.

There is a bit of heat 'leakage' from our system, even though the tank is well insulated and the boiler is right next to it.
Everytrhing is installed in a side attic, so I've converted that into an airing cupboard (works really well), and I have a home-made heat recovery system, drawing the warm air from above the boiler back into the adjacent bathroom next door. It doesn't do a lot, but it stops you getting a chilly draught when you need the fan on.

I should say, at this time of year we use almost no gas for water heating - it's all from the solar panels. It usually works like that until early October.

 

[johnny]

Is the legionella thing because of new plastic pipes? Copper is poisonous to most bacteria, and so it can't happen.

r.

no its all pipes and fittings especially where water lies stagnant for periods of time or any dead -legs of pipework where something has been removed but a spur of pipework remains. legionella grows in those areas and then contaminates all the water system which is why there are one way valves fitted to modern water systems to prevent backflow.

Copper has no effect on Legionella at all. Every owner of a building in the UK that has use by the general Public has to have a Legionaire survey risk assessment carried out by law. The risk assessment must be held in a place where it can be inspected and every water system has to be checked periodically by a qualified technician , sometimes weekly ! and the water temperature of all hot water systems has to be maintained at 60degrees .

You would not believe how many people have died in Hospitals of Legionella which is frequently put down to Pneumonia #-o

 

[Phil Pascoe]

I haven't long come out of hospital, and can vouch for the inspections. the bathrooms we used all had to have legionella filters on all outlets. This restricted the flow so badly as to render them useless, so we had to take the filters off to wash or have a shower. The shower filters would last a few days only, and were about £50 a throw.

 

[Silverbirch]

Lots of useful information here which I will do a bit more research on and quiz my plumbers about.

Very helpful. Thanks folks.

Ian

 

[Myfordman]

I'd keep it simple. If you are happy with your existing DHW in terms of flow rate/pressure and the size of the cylinder.
Then just fit a basic system boiler - IMHO Worcester Bosch Greenstar xxRi range hard to beat for simplicity, reliability and availability of spares. Easy DIY install - just use a gas-safe engineer to connect the gas and commission the system to get all the correct paperwork

If you want mains pressure hotwater and willing to wait (potentially) for the time it takes to fill a bath then consider a combi. This will lose the airing cupboard but give you increased (cold) storage space. Make sure SWMBO is happy with this!
If you are a diyer, a loop of 22mm pipe routed through the base of the cupboard and connected to your radiator circuit will restore the airing function. Don't for forget to add an air bleed point.

For absolute economy, there is no doubt that any form of stored hot water system wastes energy even with lots of insulation (my tank has 75mm of foam and loses about 10-15% of the stored energy overnight)
The best you can do for efficiency is point of use electric water heaters but you still need to run the central heating.

hth

MM

 

[Silverbirch]

Thanks MM, some useful information to add to my deliberations.
There definitely won`t be any DIY involved though. My plumbing skills don`t go beyond connecting the garden hose to the outside tap!

Ian