Hello again to watersystems/drdrivel/so many names I cant remember them all and now simonH2, nothing wrong with combis mate same as thermal stores, there are places you should and places you shouldent use them.
General Question regarding water supply
- Thread starter jal
- Start date
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Ullo Tosh - gotta Toshiba 
Building slang - a tosher is a rough semi skilled painter To tosh it in /over is to do a quick cover job without any preperation - one of the reasons Council houses were sold off - the maintenance costs were exaggerated and they were " decorated " by gangs of Toshers
Building slang - a tosher is a rough semi skilled painter To tosh it in /over is to do a quick cover job without any preperation - one of the reasons Council houses were sold off - the maintenance costs were exaggerated and they were " decorated " by gangs of Toshers You got that wrong. Combi's are bigwaterburners favourite choice.
Just seen his TS thread link . Good quality pipe work that could put many to shame. If this is diy then 10/10. As for combi's I agree with him. Biggest heaps of shyte ever invented.
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Want to elaborate on that ?
Are you disagreeing with the calculations ? Or with my suggestion as to the unsuitability of the boiler for the installation ? Or with my suggestion for a method of reducing the problem a little ? Or my suggestion that a HW cylinder or TS would be an improvement ? Or something else ?
Of course, if you have something POSITIVE to add ...
sorry for mistaking simonH2 for bigsystemburner, it was the belief that he is right and everybody else (especially anyone that installs combis) are idiots that put me on the wrong track,
simon.. you have a small flat ? with a HUGH garage no wonder you can fit everything in, try fitting that lot into some of the flats I used to work in london, the project developers would throw you off site, as a matter of interest how much were the materials you used ? combis are ok if used in the right propertys, its when numpty installers put them in unsuitable propertys that you have problems.
simon.. you have a small flat ? with a HUGH garage no wonder you can fit everything in, try fitting that lot into some of the flats I used to work in london, the project developers would throw you off site, as a matter of interest how much were the materials you used ? combis are ok if used in the right propertys, its when numpty installers put them in unsuitable propertys that you have problems.
Fair enough - we all do that sort of thing from time to time
I agree, yes I've got 'adequate' space, but that's not an excuse for most combis. I realise some flats etc are just too small - but the problem is that the developers have this mindset that they can skimp on the plumbing because a combi will work round their inability to design a building to have proper services. By now you may have guessed that I'm no fan of combi boilers
I agree with you - their use is where there is nowhere to put a F&E tank, and nowhere to put a cylinder or store. That doesn't make them a good choice, just the least worst option for a bad development.
I've always lived in a house with a hot water cylinder - you know, turn on tap, hot water comes out; turn on two taps, hot water comes out of both of them. Boiler breaks down, switch on immersion heater - no big deal.
When I bought the flat, which I bought for the garage
, this combi was an eye opener. It might have 'mains pressure' hot water, but the flow rate is crap (takes forever to run a bath), temperature control is crap (the shower cycles hot-cool-hot-cool-hot-cool...), there's a minimum flow rate which made washing the paint roller out a chilly job, and for all this it needs a boiler that is stupidly oversize (even on it's minimum burner output) for heating the flat. That boiler is almost 30kW - and it still can't do a good flow of hot water.And of course, when the boiler breaks down, you have no hot water - and no easy way of providing any form of backup. That really annoys tenants who then withhold rent.
That thermal store, with it's enclosing cupboard, is just under 2foot square. I find it hard to believe that there are many developments where that amount of space couldn't be found IF DESIGNED IN FROM THE OUTSET. Just make a cupboard a little deeper and you have an airing cupboard - well you needed somewhere to store clothes anyway ! I still have main pressure hot water, the boiler runs more efficiently (I should be able to get a condensing boiler to run in condensing mode all the time - how many can say that ?), and I have a backup when the boiler breaks down.
The big downside is the cost, which I suspect you suspected as well. The store alone was about a grand (+VAT). The mixer valves I picked up as surplus stock at £25 each. The Grundfos Alpha pump is getting on for £100 - but it lets me have a fully TRV system, no minimum flow rate through the boiler to worry about. The rest (pipe, fittings, etc) I don't want to add up
So yes, it's cost a bit. I suspect that thermal stores would come down significantly in price if they were more common - but there'll still be a premium.Thermal stores do have one or two drawbacks. This is a fully passive design and hot water is heated in a coil passing up inside the store - like a hot water cylinder swapped round. That does impose a limit to the hot water available, and if you pull enough flow rate you'd start to drop the temperature. That can be compensated for a bit by running the store a bit hotter, or in this case I've chosen a model size up which has a larger coil - not to mention that because of the limited output from a combi, they've done all the plumbing in 15mm pipe. The upside of being a passive design is that you can still get hot water with no electricity - but you will run out as the store goes cold.
Others have a plate heat exchanger (and a pump to move hot water from the store through it's primary), and cite power transfer rates of 100kW or more.
They put that in to supply a house, no wonder you have a problem
It takes 4.2kW to raise 1l of water by 1˚C per second. So lets assume you need a minimum of 50˚C temperature rise (incoming water is very cold this time of year), then the max flow rate is :
26.4/4.2/50 = 0.126 l/s, or 7.5 litre/min Not much is it !
Apart from throttling the downstairs tap, there's not a lot you can do. It has occurred to me that a pressure balancing valve* in the cold water supply might help - but only by slowing your cold supply to a dribble at the shower when the hot pressure disappears.
* I'm sure someone will correct me, but I'm fairly sure you can get a valve that, instead of regulating the pressure to a fixed level, will regulate it to the pressure in another circuit. So you'd fit this valve in the cold supply after the tee off to the boiler, and get it to regulate the cold pressure to match the hot pressure downstream of the boiler and it's metering valve.
My advice, if you have the space and cash - ditch the combi and fit a hot water cylinder, or a thermal store which can buffer the heating as well. And if any plumber goes "<suck through teeth>you don't want to be doing that" - then show them the way out.
I'll try the 'pressure balance valve' as a last resort. Would adjusting the 'restrictor flow screw' on the diverter valve make any difference?
Regards
Jal.
Well it won't solve the problem, merely mask one unwelcome side effect which is relying on the thermostatic shower valve to prevent you getting doused in freezing water when another tap is turned on, and then with scalding hot water for a short while when the tap is turned off. It will simply reduce the cold water pressure to match the hot so neither reaches the bathroom.
All it will do is increase or decrease the flow rate. If you open it up enough then you'll be able to supply a tap and the shower - but you'll have so much flow rate that it will only be tepid. Unfortunately there is no answer to an inadequate DHW flow rate from a combi - other than to fit a much bigger (and even more inefficient) combi, or fit a storage cylinder.
As a side question for those in the know about modern combi's. Do any of them have less basic DHW flow rate control than a simple fixed (but adjustable) restrictor ? Eg, do any of them have a thermostatic valve that can adjust the flow rate to automatically achieve a set flow temperature with variations in inlet temperature ?
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