Central heating boilers (again)

[oldfella]

We are about to replace our old heating/hot water oil boiler. We understand that we must have an condensing boiler.

As we wish to remove our hot water cylinder and get rid of all the pipes that are needed for this we have considered buying a 'on demand' type boiler and situate outside. I have heard conflicting stories about how good or otherwise these systems are.

Your advise, thoughts and considerations on new boiler installation would be appreciated. We are not on mains gas supply.

 

[middi]

Condensing boilers are much more efficient than standard boilers.

choose a high rating hot water emission if you need to, a combi condensing boiler has to discharge its condensed acidic emission into a purpose designed chamber or to existing sewer system, hence a little more expensive to install.

They are approx 25/30 % more expensive than standard boilers to buy.

It is also difficult to have corgi registered fitters to issue a certificate for standard boilers now, unless you have an exemption clause as to why a condensing boiler should not be fitted.

Apart from this they are very good.

 

[thiambal]

My opinion FWIW is to think very carfully before having a hot water tank removed and replaced with a combination (on demand) boiler.

The advantage with a combi boiler is that you are only heating the water you need and so it should save you money on fuel. However, unless the piping is good and the boiler has a sufficiently high output you can end up....

1) waiting ages for hot water at the tap
2) taking forever to run a hot bath
3) having trouble drawing more than one lot of hot water off at a time (i.e. you end up with a freezing cold shower if someone turns on a tap)

In then end I was so sick of our combi boiler that I had the thing taken out and a hot water cylinder put back in.

There are of course solutions to all these problems and many people swear by combi's. However, take lots of advice on the type and size of the boilers and also factor in demand caused by future expansion of the heating and hot water system for extra radiators and/or extensions.

You can get exemptions from having a condensing boiler but it is not easy - you either need a very special situation or a bent corgi installer. Opinions seem to vary on whether condesning boilder have long term durablity, cheaper models can also be rather restrictive in where and how they can be installed. There it is a case of you get what you pay for I suppose.

As far as we are concerned we have noticed a significant drop in fuel bills since changing to condensing boiler - that can only be a good thing - for the planet, and more importantly, for my pocket!

 

[geoff]

I put in a Combi when refurbishing about 5-6 yrs ago. I wouldn't recommend them at all. Unless the central heating is on, the hot water takes an age to come through - it can be over a minute, depending on the temp of the incoming.

The hot water isn't heated directly, the boiler uses a pumped heat exchanger circuit; if the c.h. is on, this water is already heated but if not, it has to heat this up first before the h.w. starts to get hot. God knows how many litres of water are wasted down the drain waiting for it to warm up (at a cost as well!). The flow controller used to control temperature and safety cutout also means it can be difficult or impossible to get a slow flow of water (the gas cuts out if the flow drops below a certain value). I find taps need adjustment more as well.

I think they are popular with plumbers for a few reasons - they are physically easier to install, no cylinder or pipe work to thread through the property (and no problems from airlocks etc.), they can charge the same for the system but with less work, it improves their spending turnover with the builders merchant and repairs can be lucrative (more time and expensive spare parts). But perhaps I'm being cynical......

I am thinking of changing from LPG to oil and putting in a thermal store for both heating and hw - far more responsive, it can reduce boiler cycling (more efficient) and you can add geothermal/solar easily.

Unless you have absolutely no room for a cylinder or thermal store, I would say avoid combis.

 

[thiambal]

The hot water isn't heated directly, the boiler uses a pumped heat exchanger circuit; if the c.h. is on, this water is already heated but if not, it has to heat this up first before the h.w. starts to get hot. God knows how many litres of water are wasted down the drain waiting for it to warm up (at a cost as well!). The flow controller used to control temperature and safety cutout also means it can be difficult or impossible to get a slow flow of water (the gas cuts out if the flow drops below a certain value). I find taps need adjustment more as well.

All true, and all things I forgot to mention. It is now coming back to me just how much I disliked the combi!

 

[middi]

The up to date combi boilers override heating requirements in favour of hot water.

 

[oldfella]

THank you for replies so far, I am being weaned away from the combi's from what is being said here and elsewhere.

We currently have a conventional oil boiler system which is almost ten years old now and altho still works fine the boiler is situated in our dining room!! Blame the previous home owner. As we are embarking upon a complete refit of kitchen and bathroom very soon it seemed the ideal time to sort the boiler problem.

We started to think about a boiler situated outside but I have just seen the effieciency ratings of these and am not impressed at all.

Its a tough choice becuase we wanted to free up the airing cupboard upstairs and install a cloakroom.(our bathroom is downstairs). Decisions :roll:

 

[monkey writer]

If going for combi condensing - make sure you get one with a stainless steel heat exchanger rather than an aluminium one as they do not corrode as quickly.

 

[Zac]

We had a combi in a property that thankfully we were renting at the time, very hard water area, two heat exchangers :?: later the landlord fitted a water softener. With this in situ hot water flow was maintained & cannot complain about performance

 

[Peter]

I believe there are corrosion issues if the condensate is discharged into your cast iron pipes.

 

[Moo]

Whatever system you have, surely there will always be a delay before the water runs hot - depending on the distance between the boiler and the tap, you first have to get rid of the cold water that's been sitting in the pipe.

 

[andilou]

We are about to replace our old heating/hot water oil boiler. We understand that we must have an condensing boiler.

As we wish to remove our hot water cylinder and get rid of all the pipes that are needed for this we have considered buying a 'on demand' type boiler and situate outside. I have heard conflicting stories about how good or otherwise these systems are.

Your advise, thoughts and considerations on new boiler installation would be appreciated. We are not on mains gas supply.

Hi,
We are looking to do the same, i think some of your replies assume that you must have a combi condensing boiler. As i understand it you can have a 'system' condensing boiler, with a 'megaflow' cylinder.
This does away with the need for pumps, and so long as your mains water pressure is adequate ( i think about 2 bar), will provide a good flow of water and fill a bath very quickly.

 

[paulbandler]

Over the past 7 years or so I've had 4 combi's installed in either my own or my parents property and concur with all the views expressed so far. One was an early condensing boiler and lasted only 4 years before corrosion did for it.

Am about to have a traditional system boiler installed (normal unpressurised hot water tank but no separate expansion tank for CH) plus a whole house pump to get good shower pressure. Reasons for choice are reliability, store of hot water allowing drawing of multiple hot water users at the same time, and the availability of immersion heater as a backup when the boiler fails (and it does, normally at Christmas...). I had considered the system + megaflow option as this provides all those advantages without the need for whole house pump, but they are a specialist install and was pursuaded by builder that a house pump would do as good a job without such a fancy hot water tank.

Having said all that, there are some advantages of combi's, particularly the fact that the supply of hot water is pretty much continuous - i.e. someone doesn't use up all the hot water in the tank causing you to need to wait half an hour for a shower... Also there are some good large combi's - the one installed at my parents place is a floor standing Worcester 400 HiFlow which has a small internal water store (as many do) and will supply multiple hot water pipes (provided you have the water pressure). Also you can consider retaining the cold water tank in the loft even thought its not absolutely necessary and use it to supply the loo's, washing machine, and non-mixing cold taps (if you mix mains pressure and non-mains pressure you can get problems, particualarly on thermostatic mixer taps - this happened at my parents place on some safety taps in the hand basin - means they wash their teeth in slightly warm water).

At the end of the day, its a trade off, but I would say that if you have the space, stay traditional. Also you can be imaginative in where you site the boiler provided you observe the manufacture guidelines - the HiFlow in my parents place was squeezed under the stairs in a small 3BR semi.

 

[sarahj]

You do not need to install a condensing oil-fired boiler until after April 2007, so if you want to choose something else do so now!

 

[finglonger]

We had a Vaillant Ecotec combi installed a couple of months ago. We wanted to remove the hideous radiant gas fire and back boiler which finally gave up the ghost the day before the installer came.

After speaking to five or six plumbers we decided to get a vaillant since they seemed to be the only ones which last (although you pay more for them). So far we have been delighted with it. The hot water actually comes through considerably faster than the tank did, as the pressure is higher (nearly mains pressure). It has to travel a good 6 or 7 metres to our shower and is there within 10-20 seconds compared to about 30-40 for the tank system. If we had removed the 22mm pipe from the boiler to the shower and replaced with 15mm it would be a lot quicker.

We've not had any trouble with running a shower or bath and filling the kitchen sink at the same time either. I think that you can get problems with water pressure - you need to have good a flow rate (10 litres a minute I think, off the top of my head but you probably want to check that before you take it as gospel). You can test it roughly by seeing how long it takes to fill a 5l bucket at the tap furthest from where the mains supply comes into your house.

Admittedly it's only been a few months (it was installed in July) but I'm delighted with our combi and wouldn't want to go back to a tank now.

 

[Johneds]

I have been dead against combi boilers for years and have always said I would never have one in my house.

However, I've specified dozens over the last couple of years in projects and this has changed my mind. The current crop of 35kW combis are nothing short of fantastic. They provide copious amounts of piping hot water and if you have good water pressure you get an excellent shower with no fandangled pumps and flow switches and things.

Search out somebody that has a 35kW one and check it out for yourself before making a decision.

 

[monkey writer]

which would you recommend?

we had an Alpha CD32C installed yesterday... we finally have hot water! Too early to say if it's any good though...

 

[thiambal]

The central heating/plumbing forum on DIYNOT is a good source of advice - and there are plenty of topics on this subject.

When I investigatyed the net Valliant were pretty much the only company that I could find little or no critcism about (cue criticism.......)

 

[oldfella]

Many thanks for all your replies which have provided plenty of food for thought. I may simply have the existing boiler re-sited for now and have another look in a few years time. On the other hand !!

 

[mark_j_k]

We are going to have a new boiler installed soon. Our hot water tank is of the Primatic type and therefore just changing the boiler isn't as straight forward.
I think we will be getting a combi installed otherwise I'll have to buy a new hot tank, cold tank for the loft and other bits. Besides, I enlarged the loft hatch a while back and I don't fancy making it even larger to pass a tank up.
I've replaced all the radiators and they are not linked up at present (we managed without ch for about 10 years so I'm in no hurry to get a new boiler)

Had a plumber come round to have a look about fitting a combi and he said that the water pressure didn't seem high enough for us to have one. We contacted the water board (they offer a free pressure test) and they came and tested it. 4 bar was what they recorded which is fine but the man said there wasn't enough water flow.

A week after the pressure measurement being done I was woken up at 6:30 in the morning with the cold pipes clanking away, went to a tap and no water came out. In the end I traced the fault to be and old valve that fed the outside toilet that had been piped onto when the lead pipe was replaced.

Now we have alot more water flow and at pressure too.