Combi boiler - 'Combisave' valve.

bacharach01 · 28 May 2010

Hello All

I’ve been looking at all of the helpful advice on this website as I’m currently considering having a “Combisave” valve fitted to the pipework feeding my combi boiler, which the company providing it are saying will:

A: Save me approx £150 per year on gas bills (based on a semi with a family of four)

B: Greatly reduce my water consumption

C: Significantly reduce the waiting time at the tap for the hot water to arrive.

The valve supposedly reduces the flow of the cold water until it’s warm enough – meaning that once the water is at the right temperature there is no loss of pressure. I’ve not been able to find anything out about this mechanism on the internet and was wondering if you had heard of it and if it does all that is promised? The company involved are a reputable firm (in my opinion).

Any advice would be gratefully received.

Regards

Andrew

ianniann · 28 May 2010

The promises are excessive but the concept is sound. You can achieve the same thing by running hot taps slowly until they warm up. The trick is whether you can train your kids to do the same

D_Hailsham · 28 May 2010

As the hot water will be too hot for comfort when it is up to temperature and will need to be mixed with cold water, just put the plug in when you turn the tap on, so the cooler water from the hot tap gets used and not sent straight down the plug hole.

I know this is not possible with a shower.

bacharach01 · 28 May 2010

ianniann said:
The promises are excessive but the concept is sound. You can achieve the same thing by running hot taps slowly until they warm up. The trick is whether you can train your kids to do the same

So in your opinion is it worth the £150? Here's the link that explains the device in more detail:

http://www.moleuk.com/molegreen.php?content=3
Thanks again for your advice!

ianniann · 28 May 2010

I'll put my money where my mouth is. I have a combi boiler and I wouldn't buy this. It saves nothing when running a bath and nothing in other situations where the initial cold flow isn't wasted. It saves relatively little in situations where you are able to turn the tap on just slightly at first, and it saves relatively little when the boiler has a preheat function.

It might be useful if you take a lot of showers and have an older boiler without preheat. It might be useful if you have a lot of kids, or other significant others, who like to run the hot tap twenty times a day just for a cup of less than ice cold water

It is probably only useful if you're on metered water, since the gas savings are largely fictitious in most circumstances.

mickyg · 28 May 2010

Probably just a wax capsule valve, can't see how its gonna save any gas ro water for that matter. If you want the water at a certain temperature, however its acheived it will take the same amount of energy. So no gas saved.
As for water? well its holding on to it until its hot, so your drawing off a trickle of cold water and there will still be a pipe full of cold to come. So not really gonna save much water.
what a pointless waste of money.

Agile · 28 May 2010

One way to save water is to turn the tap on at a lower flow rate and use the water to clean your teeth. Then increase the flow rate when the water starts to get warm.

The Potty Puma already has this built in !

Tony

TheOP · 28 May 2010

What about potential damage to the boiler.

What effect will killing the flow until the water heats up have on the boiler?

Won't it increase limescale formation within the boiler in hard water areas?

ianniann · 28 May 2010

What effect will killing the flow until the water heats up have on the boiler?

It doesn't kill the flow. If it did then the boiler wouldn't fire. Presumably it is tuned to near the minimum flow level for each boiler, or perhaps just fixed at a low flow that ought to light up every boiler. It is no different to running a tap very slowly.

If you want the water at a certain temperature, however its acheived it will take the same amount of energy. So no gas saved.

All combi boilers require a certain amount of energy as they start to warm up fully before they supply fully hot water (ignoring the contents of any pipe run and any losses warming up the pipes themselves, which are inherent to any design). While they are doing this they are only providing warm water and in many circumstances this is just run down the drain, wasting both energy and water. The heating up period may be very short in some designs that simply run the hot water directly through the heat exchanger, but a very common design in newer condensing boilers contains several litres of water circulating continuously between the primary heat exchanger and a secondary heat exchanger. Without any energy being drawn away to provide luke-warm water, this may take around 30 seconds to warm up to the set temperature. If a high flow rate of cold water is running through the secondary heat exchanger and away down the drain, that may be a lot more than 30 seconds and a lot more gas and water could be wasted.

If the primary circuit is maintained permanently at a set temperature by a preheat function then there is no warmup time (at the pipes, if not at the tap) and the valve is completely useless.

mickyg · 28 May 2010

thanks for telling me how a combi boiler works, there was me wondering

Agile · 28 May 2010

TheOP said:
What about potential damage to the boiler.

What effect will killing the flow until the water heats up have on the boiler?

Won't it increase limescale formation within the boiler in hard water areas?

Limescale is only deposited at temperatures exceeding about 60°C.

By that temperature the thermo valve would have opened.

Tony

Boilerman2 · 29 May 2010

My combi dosn't have a fangled valve on it and heats up pretty damn quick! (Remeha 35c) when fitting a combi always fit a good n

Kevcarrol · 4 Jul 2010

Andrew

I don't know if this helps but I have had one for a couple of years fitted, one of the early ones. It has been great both on reducing water and gas used,particularly with two teenage kids in the house. It does what is says on the tin as they say in the advert. We also have British Gas service the boiler each year and they seem completely happy with the fitting.

I'd say try it it worked for me!!

Kevin

Bodd · 6 Mar 2011

I met the fella who invented it at an expo at Excel

Alls seems very interesting to me.

Problem is they want £80 + the vat for the unit. Don't leave alot for us to put on to make it tempting for the customer.
Then we have to go and sort it out if it cronks out.

Love the idea but don't think I'll be installing one untill its tried and tested, cheaper and asked to fit one.

Bod

Nige F · 7 Mar 2011

you`d be better off fitting it to your car fuel line - what with the price of petrol and Gadafi not going

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Combi boiler - 'Combisave' valve.

Bodd

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