Combi boiler - how big/which one?

[Ambra]

Hi,

this is my first post, so please, be gentle.

We are in the process of buying a house we currently rent and one of the first jobs we need to do is change the boiler, as the current one is 20+ years old, and I can tell you it is really inefficient. (I think it was rating G when I checked it, but can't remember model name now). We had heating 24/7 this winter and still ended up with the ice on the inside of the patio door not melting away all day!

Also, we want to go from conventional to combi boiler, and get rid of the hot water tank, and header tanks in the loft.

The house is detached, 4 bedrooms, 1 bathroom + ensuite. (No utility)

Now, I know that some people don't like combi boilers, but we decided it is the way forward for us. By trying different calculators, I found out that 19kW would be sufficient for the heating needs of the house, but from reading around, it looks like 35KW would be suggested to deal with hot water demand.

I like to sound of EcoTec plus 937 with a small hot water buffer, it sounds like it would be able to deal with hot water demand if one of us is taking a shower whilst someone opens the kitchen tap, for example. One thing that bothers me - it is huge.

Another one that looks interesting (and a bit less intrusive) is Viessmann Vitodens 222-W, but I can't find much information about it. It looks like it has 46l primary cylinder, but I can only get more info on the floor-standing model, not the wall mounted one.

Does anyone have other recommendations? Do we really need an integral hot water storage/buffer? Any models to look out for and how to find a reliable engineer?

Any ideas of costs involved?... I think we will be replacing radiators at the same time, so that we end up with clean system (and no repainting). (There are 12 radiators of varying sizes)

 

[Beerlover]

Please forget the Vaillant 937 lots of reliabilty issues and will only give the claimed 20 l/min if a blender valve is fitted and your incoming main is up to the job (25mm MDPE recomended). the 837 will do the job and is apparently the most efficient on the market -sic Viessman rep.

Veissman another good choice.

re patio frost: are the radiators on the outer wall ie under the windows?

Cheers

 

[Ambra]

Yes, most radiators are on the outer walls (apart from kitchen, cloakroom, hallway and landing upstairs).

For the patio door frost. It is in the dining room, room size is about 2.5m x 3.1 m, the radiator is on the wall adjoining the side wall (external). The doors are old, sliding type with metal looking frame, and I am sure they need replacement as at any other time of the year as soon as the sun heats up the doors, they mist inside. The temperature in the house during the winter was 18-20 C even with the heating 24/7. The windows are double glazed.

Yes, we have lots of work planned for the house once it is officially ours.

 

[David937]

Please forget the Vaillant 937 lots of reliabilty issues

What sort of issues does it have?

 

[gas4you]

Have a look at the ATAG 'Q' series, or slightly less powerful, but a lot more efficient, the ATAG A325EC.

Failing that, I would rather install the Broag Avanta Plus 39c, than the 937.

 

[Beerlover]

F81-F91 faults - vaillant cure is new pump (b*tch to change), loom (B*tch to change as boiler off wall) and little pcb top right of boiler.
Also 'con' errors - main pcb,display & little pcb changed simultaneously.

Do you want to tell a customer the cost of repair ex-warranty ? You will also need lots of clearance for the repair. Most I have seen are hidden in larder cabinets.

Cheers

 

[David937]

F81-F91 faults - vaillant cure is new pump (b*tch to change), loom (B*tch to change as boiler off wall) and little pcb top right of boiler.
Also 'con' errors - main pcb,display & little pcb changed simultaneously.

Do you want to tell a customer the cost of repair ex-warranty ? You will also need lots of clearance for the repair. Most I have seen are hidden in larder cabinets.

Cheers

Oh dear

I hope our own does not develop this fault, it is going to be 2 years old next month and out of guarantee

 

[D_Hailsham]

The house is detached, 4 bedrooms, 1 bathroom + ensuite. (No utility)

By trying different calculators, I found out that 19kW would be sufficient for the heating needs of the house ... .

19kW sounds a lot for that size house- unless it has no insulation at all; and if it doesn't, the first thing you should do is insulate it. This will bring down the heating requirement considerably. Use Energy Savings Trust Grant Search to find the cheap/free deals currently available.

Use the Boiler Size Calculator, it's the most reliable.

Don't forget that, with a combi, all water is supplied from the one source - the incoming cold mains. So if you are under the shower and someone flushes the toilet or starts the washing machine etc etc, you will notice it as a reduced flow rate, change of temp etc. You also do not have any back-up immersion heater when the boiler goes wrong.

I paid a visit to the show houses of a new estate nearby. The were all four-bed and, without exception, they all had a system boiler and a Range Tribune cylinder.

You say that you think a 35kW combi would be suitable for the hot water. What is this based on? Is it the cold water flow rate at the kitchen tap?

 

[htgeng]

slightly less powerful, but a lot more efficient, the ATAG A325EC.

.

Another vote for the A325EC. A beautifully made boiler and unlike most others all parts are easily accessible from the front. Hot water supply is almost as good as a 40kw boiler.

 

[Ambra]

Thanks all. I will have a look at model suggested.

I am not sure of the wall insulation (house built 1988), so I might have selected the wrong value for that. Anyway, from what I read so far, for combi it is the hot water supply that usually rules what power boiler to choose.

I have tried measuring the cold water flow at the kitchen tap, and it worked out at about 16-17l/min. However, I am not trusting this tap, as I think it might be a bit 'clogged'. For example the hot water flow (from the cylinder) is much lower. Cold water flow in the bath seems to be much more higher, although I haven't measured that. Will give it a go maybe tomorrow.

 

[mehran]

I would recommend a 36kw Intergas combi... fewer moving parts, compact and one a very few boiler that can condense on hot water fully. really fantastic boiler.

if your need are greater than a combi and you dont want a tank then I would go for a rinnai 26i water heater and system boiler(intergas again for the system boiler)

 

[gas4you]

slightly less powerful, but a lot more efficient, the ATAG A325EC.

.

Another vote for the A325EC. A beautifully made boiler and unlike most others all parts are easily accessible from the front. Hot water supply is almost as good as a 40kw boiler.

Most efficient domestic boiler on the market at present, hot water mode and heating

 

[compheat]

I also would recommend the Intergas 36/30 HRE for exactly the same reasons

 

[Agile]

Everyone wants to recommend the Intergas but I wonder how many they have actually fitted. They use a four pipe heat exchanger but the bore of the DHW is only about 8-9 mm and would be a prime candidate for scaling up with a dripping tap.

There is a German fellow at the UK Viessmann who seems to know their boilers quite well.

Tony

 

[mehran]

I install intergas boiler but live in a hard scale area, I believe parts of Holland were the boiler is made and developed are hard water area. even if it did scale up because it is a single copper pipe and not a plate HX it would respond very well to chemical flushing. not too worried

the only problem I see is that because it is unique product and the other boiler manufacturers cant easily copy the HX design with out violating patents. then I suspect the only other course of action for them is to spread FUD.

IMO intergas is the pinnacle of domestic combi boiler design. it does more then other boilers with less parts over all and less moving parts.

not to say viessmann boilers are bad of course....