This time it's about gas boilers

[Moo]

The boiler installed by the cowboys who 'did' our son's house just over five years ago has had its umpteenth visit by the British Gas chaps (thank goodness the poor lad took out BG insurance, otherwise he'd have to remortgage the house).

Anyway - it's all gone beyond a joke, a replacement boiler must be found, and where better to get honest expert advice than PPUK?

The current disaster is one of those that operate like an old-fashioned gas geyser (I've just had a senior moment and the proper name escapes me) and the new one will have to operate in the same way.
What would be the greenest, and cheapest** make and model to instal and maintain ?

** That's a Very Important Factor!

 

[Nemesis]

Ascot geyser?

 

[Lime]

Multipoint?

 

[tony]

The boiler installed by the cowboys who 'did' our son's house just over five years ago has had its umpteenth visit by the British Gas chaps (thank goodness the poor lad took out BG insurance, otherwise he'd have to remortgage the house).

Anyway - it's all gone beyond a joke, a replacement boiler must be found, and where better to get honest expert advice than PPUK?

The current disaster is one of those that operate like an old-fashioned gas geyser (I've just had a senior moment and the proper name escapes me) and the new one will have to operate in the same way.
What would be the greenest, and cheapest** make and model to instal and maintain ?

** That's a Very Important Factor!

Its probable BG fifth visit, because they cannot fix it the first time around and then want to charge you about £2500 for a boiler swap.

If you are getting the boiler swapped and are keeping the existing pipework to the radiators, please ask them about a chemical flush added to the system and a power flush to the existing pipework

regards

tony

 

[Penners]

Moo - I don't know whether this might be of any help.

 

[Moo]

I've remembered the name - it's called a combi boiler.

Is it possible to get one that's also condensing (as recommended on the Energy Saving Trust site) ?

Tony - I've passed on the advice about flushing the system, but am a bit alarmed about the prospect of £2500 for a new boiler. Is that the sort of figure we should be expecting for a reasonable job?

 

[tony]

No, thats not a reasonable sum, but my next door neighbour was quoted that sum of cash.

1st visit, a while before boiler change, add chemical flush to system( only required if its just swapping a boiler over, and not replacing pipework), this will give nasty chemicals a chance to soften up deposits in radiators, pipes etc.

2nd visit strip out old bolier , alter pipework to suit new boiler connections, flush out system. fit new boiler, commission boiler, cold, hot flush using boiler pipework, pour nasty chemicals down drain when draining system down,

Condensing boilers are good, but remember if your connecting to existing pipework you might not get the most out of the system as the old pipework might be incorrectly sized , run, insulated.

You might want to consider a system boiler if you have are a regular bath user than a shower user, as some combi's can be a bit slow to fill a good size roll top bath.

happy googling

regards

tony

 

[Aidan]

I've remembered the name - it's called a combi boiler.

Is it possible to get one that's also condensing (as recommended on the Energy Saving Trust site) ?

Do a search on some of the plumbers'/ heating sites or Uk-diy
The regular recommendations are Vaillant and Worcester Bosch.

Conbi boilers have a whole pile of additional components shoe-horned into a wall-hung boiler sized casing. The maximum amount of assembley work is done in the boiler factory and the minimum on site. They are mis-sold more than endowment mortgages. They can be a real PITA when they start going wrong.

If you get a modulating (variable heat output) boiler and a compatible room temperature sensor supplied by the boiler manufacturer (not a thermostat) then the water flow temperature will drop to the lowest possible and the boiler will operate at higher efficiency condensing mode for much longer. Plumbers often don't understand these things.



[/quote]Tony - I've passed on the advice about flushing the system, but am a bit alarmed about the prospect of £2500 for a new boiler. Is that the sort of figure we should be expecting for a reasonable job?[/quote]

£1,800 upwards I'd guess. Don't let BG do it, get a local Corgi.

 

[Moo]

Do I just google "plumbers'/ heating sites" ?


"They can be a real PITA when they start going wrong." - like our son's !!
But on the other hand ours (a Worcester Bosch combi) has been trouble-free for nigh on ten years now.
In fact it was because ours has been so good, and has coped so well with our two showers, that we persuaded son to get rid of the tank in the loft and go for a combi (nobody uses the bath in his house; young people these days just dash in and out of the shower).

 

[Lime]

The reports I have read and been told do not make me want to go out and buy a condensing boiler.
Most appear to be expensive to buy, install and maintain.
Maintenance appears to be the biggest problem as it is required much more regularly than with other boilers that can/could be "forgotten" for a while.
The 90% efficiency figure is also somewhat a phantom figure as it is often never achieved in practice.

Remember a combi boiler is not necessarily a condensing boiler.

However I don't think you have much choice (legally) now, it has to be condensing.

Odd isn't it that a huge number of ordinary boilers are still sold even though they should not be legally installed?
Perhaps it is saying something about condensing boilers.

 

[Nimster]

Hi
We currently have a combi boiler that's on it's last legs. We've had a quote for a replacement combi condensing Bosch boiler, with digi thermostat, radiator thermostats and a complete system flush of around £2k. The boiler itself is around £1k, and the gas man reckoned on around 2 man-days work to flush and fit the new stuff. Get a couple of quotes from local Corgi gas engineers - BG are notoriously expensive.

 

[Aidan]

Do I just google "plumbers'/ heating sites" ?)

Some favourite UK ones are;

http://groups.google.com/group/uk.d-i-y/topics

http://www.diynot.com/forums/viewforum.php?f=7&sid=03cd0c2edf961f434b5669d81c4cbe53

http://www.screwfix.com/talk/forum.jspa?forumID=25

The questions have been asked before, so search the archives.


"They can be a real PITA when they start going wrong." - like our son's !!
And everyone else!

But on the other hand ours (a Worcester Bosch combi) has been trouble-free for nigh on ten years now.

You're doing well.

In fact it was because ours has been so good, and has coped so well with our two showers, that we persuaded son to get rid of the tank in the loft and go for a combi (nobody uses the bath in his house; young people these days just dash in and out of the shower).

You've now got to have a condensing boiler, due to the energy efficiency regulations unless you can claim an exception under a few cases.

Combi boilers work by diverting the heated water through a secondary heat exchanger when a hot tap is turned on. This allows them to be connected directly to the mains, so they have advantages and are a necessity in flats.

However, it also accounts for the two main problems with them;
1) Low hot water flow rates
2) Secondary heat exchanger fouling

Low hot water flow
The boiler is sized for the heating load, lets say 20kW for a 3 bed semi. Unfortunately 20kW or so equates to a feeble flow rate when converted into heating mains water from about 10 to 60 degC. OK for one shower, rubbish for 2 showers or a bath if it takes 15 minutes to fill it. A conventional storage cylinder stores the heat required over an hour or so and might take only 5kW of the boiler output to do so. With the combi the central heating goes OFF when the hot water is being used. To get around this, 40 or 45kW boilers are being fitted where a 20kW boiler was previously adequate. You might need to upgrade the gas pipes and/or meter to fit one of these.

Secondary heat exchanger fouling

The secondary heat exchangers used are a type called brazed plate heat exchangers (BPHE). They're made by pressing channels into brass plates and brazing a stack of the plates together. Boiler water flows through one set of channels, mains water flow through another set. Heat is exchanged through the plates, but the water streams don't mix.

The thing about BPHEs is that the water ways are NARROW; they block easily. In hard water areas the secondary HWS side is liable to block with lime-scale, unless you have an ion-exchange softener (no, not those Mickey Mouse electric/ magnet things) or a combi-mate phosphate water conditioner. The HE can be acid descaled, but it costs money and they can get so blocked that the descaler can't be pumped through it.

The primary boiler water side is liable to block with corrosion products from the heating system, especially if the boiler is fitted to an old system with a history of corrosion problems. Most manufacturers specify power flushing before fitting the boiler, but you can't guarantee that a proper power flush will shift all the deposits. I'll guarantee that it won't. Some installers demand new radiators and pipework.

I'd stick with a cylinder, if you've got room. If you haven't, I'd get a Vaillant combi. Specify the boiler you want. A recommendation from an installer is usually the boiler on which he has the highest profit margin.

 

[dormouse]

But on the other hand ours (a Worcester Bosch combi) has been trouble-free for nigh on ten years now.

Our boilerman said that he would recommend Valliant as the best. He also said that he'd have recommended Worcester Bosch up to about 3 years ago, but not now.

 

[Nimster]

Hi

We had another quote for our new system. The second guy also recommends Valiant. He said the heat exchanger in the Bosch boilers is made of aluminium (Valiant is stainless steel) which, he thinks, degrades due to the acid condensate produced.

He has contacted Bosch about this, but they're insisting the boilers are fine, even though he opened up the trap on one to find it full of a fine grey "sand".

Whether it is, or isn't, aluminium I'm not sure, but he's refusing to fit any more Bosch boilers until they replace the heat exchange with steel.

 

[Lime]

not all stainless steel is the same either.
Some can pit quite badly.
My stainless steel Bosch dishwasher that died 5 years ago had rust spots all over the steel every time it was used.
If they weren't removed they became pits.
My present Candy dishwasher (half the price of the Bosch and also stainless steel) is always spotless.

However I don't think aluminium is a good material to use in a condensing boiler. The condensate is usually acidic.

 

[Aidan]

Hi

We had another quote for our new system. The second guy also recommends Valiant. He said the heat exchanger in the Bosch boilers is made of aluminium (Vaillant is stainless steel) which, he thinks, degrades due to the acid condensate produced.

Interesting, I didn't know that. I've looked it up and I think you're right. I'm not keen on aluminium anywhere in heating systems.

I believe (I may be wrong) the Vaillant stainless steel heat exchangers are made by Gianonni and sold to boiler manufacturers all over. The heat exchangers shown in some foreign boiler diagrams are very similar-looking to those in some UK boilers.

The Viessmann boilers are also very good, I'm told, but they haven't sold many in the UK and are expensive. I've no first hand experience of them.