Love or Hate your Combi Boiler - advice appreciated

inmypocketnottheirs

tm9 wrote: »

Why is that? Is there any other system you would recommend? We have a problem in that our airing cupboard is really small. The thick insulation on the latest new cylinders would only leave us with about 14 inches across for the actual cylinder and I am not sure where else we could locate it. However, if the combis are not good then I guess we might have to look in to this further.

Thanks so much for the info.

Primarily I like to have stored hot water. Boilers, including combis, can and do breakdown. The idea of anything from a couple of days to a few weeks without any hot water is not appealing. Plus combis are ideally suited to single person dwellings where there isn't the demand for hot water, and less demand for heat and hot water at the same time.

How about fitting a slimline hot water cylinder http://www.plumbnation.co.uk/site/oso-15-slimline-direct-unvented-hot-water-cylinders/? Is there space in a built in cupboard or a spare bedroom to fit a new airing cupboard. Also, possibly, how about in the loft?

I'm sure the cylinder issue can be resolved.

david29dpo

Just changed to a combi from a stored gravity boiler.
My only worry is if the boiler breaks down you end up with nothing. At least with the old cylinder we could use the immersion.

aliasojo

We got rid of our hot and cold water tanks and got a combi. Best thing we ever did. We bought a higher spec model than was advised simply because of the better flow rates.

We also had a combi linked shower and an electric one so that if the boiler ever conked out, we could still wash.

We're in rented accommodation right now and we're back to water tanks. There's never enough water for all of us, the hot water runs out quickly.

Combi's for me every time.

stormbreaker

Renewed ours about 5 years ago. Moved the boiler into the loft. Shower is fine, infact quite powerful much better than our sons electric one in the main toilet. I have a bath almost nightly and no problems filling it.

The only prolems come when someone is running another tap. This has an effect on the pressure of both being used. Not a great problem unless someone decides to fill a basin of water in the kitchen when I am in the shower!!

No problems in winter.

My sister has had her combi for years and the water pressure in her hot tap is dire. I expect it all depends on the boiler output etc.

diywhynot

Love my unvented cylinder...lots of hot water at mains pressure for 2 bathrooms....but also loved the combi in my old house (1 bathroom). You need to get a RGI to take a look as he/she will be the only one among us to see the job.;)

tm9

diywhynot wrote: »

Love my unvented cylinder...lots of hot water at mains pressure for 2 bathrooms....but also loved the combi in my old house (1 bathroom). You need to get a RGI to take a look as he/she will be the only one among us to see the job.;)

Thanks to everyone for all the advice and info. The reason for asking about combis on the forum is that we had four companies in last week to take a look and all recommended different solutions - so we are confused! BG suggested a 'traditional' vented system with a 'bullet' cylinder (due to small size of our airing cupboard) and expansion tank in loft. Independent 1 and 2 recommended combi and Independent 3 recommended megaflow downstairs in utility room alongside a system boiler ???? The combi sounds ideal but we are concerned that the outside water pressure is out of our control and could change and that the boiler would have to work hard if the temperature outside was very cold? I guess we will have to just keep researching this a little further. Thanks again

alleycat`

Option 3, the system boiler, is similar to the open vent system but it doesn't have the tank in the loft.

It is a sealed system, like a combi, but with a hot water tank (the megaflo).

Assuming it comes in at a decent cost and you have the space it'd probably be the option i'd go with.

aelitaman

tm9 wrote: »

Thanks to everyone for all the advice and info. The reason for asking about combis on the forum is that we had four companies in last week to take a look and all recommended different solutions - so we are confused! BG suggested a 'traditional' vented system with a 'bullet' cylinder (due to small size of our airing cupboard) and expansion tank in loft. Independent 1 and 2 recommended combi and Independent 3 recommended megaflow downstairs in utility room alongside a system boiler ???? The combi sounds ideal but we are concerned that the outside water pressure is out of our control and could change and that the boiler would have to work hard if the temperature outside was very cold? I guess we will have to just keep researching this a little further. Thanks again

I have a large combi the largest combi that worcester bosch made at the time it was installed 2004.

First off I think the decision comes down to space available I had a traditional system and where the hot water cylinder was I wanted to put in a cloakroom. So then there was no space to house the cylinder the combi decision was made for me.

With my large combi it will comfortably run two taps at the same time. Also when is is minus 10c outside it does not falter with heating the water it still gushes out in copious volumes very hot, there is a decrease in flow rate from the summer but it still runs two taps.

Also during that time the water board upgraded the pipes in the road and the water pressure went up, so I can not see your pressure falling unless there are large numbers of house added to the water supply that you access.

There are pros and cons I have had the flue fan fail in the 8 years that it has been operational and I was without hot water and heating for 2 days. But you do not really get very smelly in 2 days.

So any of the systems proposed will provide you with hot water and heating as long as the boiler (both combi and system) are sized correctly (Kwh).

So then it is down to you.

Can you live with out hot water for 2 days if answer no then get a hot water tank system
Do you have the space for the tank? if no get a combi.

The only additional one for you is because of the small space for the tank will the hot water cylinder hold enough hot water for you now and in 10 years time.

Those are the three most important questions because I do not believe one system is more efficient than the other.

PaulF81

megaflow for me too.

Cardew

aelitaman wrote: »

I have a large combi the largest combi that worcester bosch made at the time it was installed 2004.



With my large combi it will comfortably run two taps at the same time. Also when is is minus 10c outside it does not falter with heating the water it still gushes out in copious volumes very hot, there is a decrease in flow rate from the summer but it still runs two taps.

Your solution brings us to the classic dilemma!

With modern condensing boilers it is apparently a big mistake to over-size boilers. All of the technical advice I have read states that the boiler output should be matched to heating demand to keep the boiler in condensing mode.

What size of Boiler do I need?





Old boilers may have their output measured in British Thermal Units per hour
(Btu/h), but all current boilers are sold in the metric equivalent of kilowatts
(kW). The calculator below will give the approximate metric value, but you
should bear in mind that in the past central heating engineers often installed
boilers that had a higher output than strictly necessary. Although this meant
that there was no possibility of the boiler failing to meet the demand for heat,
even in the most arctic of conditions, it also meant that they were mainly
operating at a part load, and so running below their maximum efficiency. If you
have installed additional loft or cavity wall insulation since the last boiler
was fitted, it is highly likely that you will need a smaller boiler than
before.

Sizing the condensation boiler to your home is quite important, a condensing
boiler sizing guide can help you in the right direction as to which boiler to
choose. It is very common that a replacement boiler will be sized correctly. An
over-sized boiler is more expensive to purchase and will result in higher costs
to operate because it is not running efficiently in a smaller space. It will
also cause more unnecessary emissions into the atmosphere.

Read more: http://www.doityourself.com/stry/a-condensing-boiler-sizing-guide#ixzz24DRejrSw

So it seems that getting a oversize boiler(in output) to satisfy hot water demand, will lead to lower efficiencies when heating.