Most reliable combi boiler 2011

[John Rumm]

We have a conventional storage system at the moment - takes about half an hour to fill a bath!

[Dave Plowman (News)]

It depends on many variables. There are header tank systems around with not enough head - but round here the mains flow rate is poorer than some.

I can't see why you'd want to top up a bath anyway if it's filled with the temperature you want to start with. But even if you did, any decent storage system should be able to. With a fast recovery cylinder your boiler can heat the water nearly as fast as a combi does.

Basically, no instant water heating system can cope with the possible

*peak* load/flow in the average house. A storage system can.

[Dave Plowman (News)]

All that says is it's poorly designed.

[Triffid]

I accept that there are pros and cons for both systems. And whilst a combi system may suit one household - it may not suit another.

All I can do is repeat that it is now three years since we switched from a storage system to a combi - and we have had no problems and no regrets. But there are only two of us in the house - and only the one bathroom.

[John Rumm]

Well actually it tells you that it is not appropriate for the property. No amount of design could really make it work well. There is only about

4' of head over the bottom of the bath for example, so if you lift the shower attached to the bath taps much above waist level, the water flow stops altogether!

At some point it will get ripped and replaced with a mains pressure system. I have not yet decided exactly what type. Unvented cylinder, and system boiler is one possibility, or an unvented cylinder and a combi[1] might actually work rather well. Cylinder supplying baths and showers, and combi in the utility room feeding the kitchen and utility room taps

- giving a short dead leg and pottable hot water on tap in the kitchen.

Mains flow rate and pressure here is into the firehose level of performance as well, which means there are plenty of options.

[1] Assuming one exists that can handle split temperature operation, multi zoning, and weather compensation.

[Andy Dingley]

Rubbish, and has been for decades.

We're running what might be the world's oldest Worcester Bosch combi (there's a plaque on it from the Newcomen Society) and that fills a bath just fine. Sure, the first combis had capacity problems that made them a problem for filling baths, but that's way in the past now.

[Andy Dingley]

Reliable boilers from reliable makers are reliable, whether they're combis or not. Unreliable boilers are unreliable no matter how simple. Whilst there obviously is some correlation between complexity and unreliability, this is far overwhelmed by the differences from their manufacture.

[Andy Dingley]

I have some sympathy with this view, but are you going to nip into your Tardis and go back to tell Thatcher not to build our energy generating capacity on gas too? If you follow the web links that TNP has been posting lately, it's amazing just how much of total grid output has been coming from gas of late.

If the gas is finished, or if Putin turns the tap off again, not only will the heating go off, but the lights will too.

[The Natural Philosopher]

And you had better hoe that yior electric heating doesn't run on windmills.

Unless you build a month capable thermal store.

[Dave Plowman (News)]

Yup. With our own supplies diminishing. Which would have been better used for things it does best - like domestic heating etc.

Wonder how long it will take to build up the coal mining industry again? And of course to persuade anyone to work in them will need very high wages. Now that the family history of working in mines is gone.

[The Natural Philosopher]

Sadly its also the best fast start backup technology for power generation, apart from hydro.

Arguable electricity is the best technical solution to home heating.

The only issue is poor thermal efficiencies at the power stations.

[Andy Dingley]

"Electricity" is never a "solution" to anything. Electricity needs to be generated, so the only solution can be an overall view of electricity, its generation, transmission and use.

Now comparing the relative efficiencies of electricity generation from gas + long distance grids to piping gas for heating in the home more directly is left as an exercise for the reader.

[The Natural Philosopher]

Oh don't be silly.

AT THE HOUSE electricity is the smallest lowest capital cost and mots efficient heating source of anything,.

You might as well say 'hot water is no solution to central heating.

Really!? Go on, astound me more!

Sure, and carbon free electricity at modest capital cost and hifgh reliability is easily achieved

Who is talking *gas* generation for home heating?

[John Rumm]

The usual problem is people buying on price and installers under speccing them.

[John Rumm]

One interesting avenue for improving that:

[The Natural Philosopher]

Calculate what e.g. a 500 mains pressure liter tank fitted with twin

22mm feeds to two baths can do in terms of hot water flow rate: then calculate how big a combi you need to match it.

Now calculate which costs more, and takes more space...and will be less efficient as a central heating machined because its wildly over specced for that purpose.

Combis are, basically, rubbish. Any attempt to make them work adequately, makes them bigger, more expensive, and less efficient than a system boiler + PHW tank..

[The Natural Philosopher]

All the 'con' is in the combi.

The only thing going is that they are cheap as long as you can handle a thin trickle of hot water to one hot tap or shower at a time.

[The Natural Philosopher]

Rather scary temperatures and pressures in that.

Mind you *any* form of large power or large energy storage is pretty scary.

Now how about that pint sized, sealed for 30 years life, home nuclear CHP reactor.. :-)

Any excess heat is pumped into the ground in summer, to make sure you have a good 'battery' for the winer heat pump..

[Mark]

unless it's installed in an earthquake zone

[John Rumm]

If your rising main can only deliver 15 lpm, then a 35kW combi will match it. (unless you also stick a 500L accumulator in front of the cylinder!)

Yes of course you can design a storage system that will outperform a combi - but that is hardly the point in most real world situations where space and cost are also considerations.

Hardly matters these days. A decent combi will run 10kW lower max power on heating in the first place, and then modulate down to a third or a quarter of its maximum heating output.

The one I used last time could deliver 35kW to hot water, 25kW to heating, and modulate down to about 8kW on the heating. Some will go as low as 4kW.

System boilers are basically combis anyway. Many makers use exactly the same components and design for their system boilers as they do the combis - all that is omitted in the final build is the diversion valve[1], and the PHE.

[1] Some split temperature system boilers also have a diversion valve to facilitate separate water paths for cylinder reheat and rads.

Horses for courses.