The trouble with combination boilers – a new gadget to potentially save water and energy!

I upgraded my old dilapidated combination boiler about 4 years ago for an ultra efficient condensing variety.  And, fair play, it has worked very well ever since with no issues.  Indeed, at a recent efficiency check carried out by my plumber, it hasn’t lost any of its efficiency in the intervening years.  But, there has always been one aspect of a combination boiler that has bothered me – and that is the length of time it takes to warm up water for that first shower of the day, or when you are washing up and have not used the hot water tap for a while.

I haven’t quantified exactly how much water I have to waste whilst waiting the the shower to get hot, but it is at least a minutes worth before the water has sufficiently warmed for me to get in it.  Similarly with washing up, the waste of clean water down the sink whilst waiting for it to get warm enough to wash dishes in is criminal, and as I’m also on a water meter, it’s a waste of money too.

At one stage I was collecting the shower water in a bucket and using it to water the indoor plants, but there is only so much of that you can do.  So I’ve often pondered that there should be a solution to this dilemma – and one not involving going back to a boiler with hot water tank, which can be equally wasteful of gas if you do not use the hot water that it regularly heats up in the hot water tank whether you need it or not.

Anyway, my wonderful plumber John, of Aqueous Plumbing (a south London based company if anyone is in need of a good plumber), has alerted me to a potential solution.  It’s called a ‘Combisave’ and it claims to reduce the water flow at those crucial times when the water is heating up from a standing start – this, according to their website, saves not only time in getting your hot water quicker, but both water and gas too.

The claims on the website, for a monetary saving for a family of 4 in a typical household, are quite ambitious.  Apparently, they claim you can save:

 – £55 on your hot water bill, but that could be as much as over £100

– if on a water meter, then the savings here are quoted at  £180 per year.

I have a few issues with these figures, as they seem to be based on each one of 4 family members using a hot water tap and/or shower 7 times each a day (28 uses of hot water per day in total – more than 1 use an hour!) – and each time having to wait a minute for the water to heat up!  My big issues with these assumptions are, if as in most normal households, especially on weekday mornings, the showers are taken in quick succession, then the water will not take up to a minute to heat up for all 4 showers, only the first one, after that the hot water is instantaneous as it is still warm in the pipes.  So their claim that a 4 person household can save 55,000 litres of water a year seems very optimistic to say the least.

But if it saves just the first 6 litres per day of the family’s showers, then that’s an annual saving of around 2200 litres of shower water.  Then you can add maybe another 6 litres waiting for the water to warm up when washing up in the evening (in non-dishwasher households), so that saving could presumably be doubled to about 4400 litres per year.

This could save you about £14.50 per year on a water meter (using 0.3pence/litre – their figure).

I’m not clear how to calculate the gas saving in this situation, but if we take their optimistic figure for a gas saving, and divide that by 12 (this is the reduction in the water saving given what they have calculated versus what I estimate it could be, ie 55,000/4400 litres = 12 times smaller) that gives a yearly saving of 1650 kWh/12 = 137.5 kWh.  Typical price of gas is currently around 4.5pence.  Hence saving in gas could be £5.50.  Giving a yearly combined saving in gas and water bills of about £20.  This might be a conservative low end saving, but I think its more realistic than their £200 – 300 saving figure

So, given a Combisave costs around £90, and then you will have fitting costs too ( it has to be fitted by a qualified plumber) of around £50 upwards, then we are looking at a payback, if you are on a water meter, of around  7 years.  I’m not sure how long a ‘Combisave’ is made to run for, but if it’s a ‘fit it and forget it’ device, and the lifetime is longer than 7 years, you will eventually make your money back – but most importantly, in my view, you will be doing your bit to save water in these drought-ridden times.

I’ve been monitoring my daily water and gas usage over the last week, and will be getting one of these fitted by John my plumber soon.  So watch this space for a review of how much it is actually saving me.

Want to read the results of my first month of use? Click here:

5 comments… add one
  • jennifer June 4, 2012, 1:37 pm

    Wow that sounds brillant because I have the same problem with having to let the water run till it gets hot. I was doing the same thing with saving the cold water for the plants but that gets old real quick at 6am.
    Great idea, thanks for sharing!

  • Adrian June 28, 2012, 11:06 am

    What it doesn't do is solve the hot water pipe draw length problem. You still waste what is left standing in the pipe and the energy used to heat it. I have sometimes wondered whether it is better to fit an instant heater under kitchen sinks and that electric showers aren't always a bad idea i.e. heat the water at the point of use.
    One rather smart solution to energy saving I saw at Ecobuild this year was 'shower heat recovery units'. These are heat exchangers that use the waste water from the shower to preheat the incoming water to the heater/boiler. Not cheap and they require 2.4m height to install, so best suited to new build. Could be used as well as a combisave.

  • Jeff Stockdale November 28, 2012, 9:23 am

    Whatever system you install in your house there is always the cold water in a dead leg of pipe from the hot water source to the draw off point. In a conventional stored water system its easy to eliminate this problem by fitting a secondary return from the furthest point back to the hot water cylinder by way of a bronze pump. When you open a hot tap its hot straight away. With a combi its different becuse the boiler relies on the tap opening to fire up the boiler. So itsbetter to have the boiler near the bathroom rather than a long way from it. Fitting these devices ( combisave ( isnt ereally saving you anything as it interfres with the flow of water out of the boiler SO technically it can invalidate your warranty and the boiler could fire up and off many times  because of the restricion. The old potterton Puma had such a device in the boiler, it was rubbish thats why they are all being ripped out and replaced now. Better off with a decent boiler with eco on it i.e. the Worcester Bosch 30 s.i. or the Baxi Main 30 eco models. They fire up every 30 or 40 minutes on eco mode and have 1 litre of hot water stored in the boiler.

    • Dave Furlong April 5, 2016, 4:18 pm

      Hi Jeff. Just need to correct a few points. The CombiSave doesn’t interfere with the boilers warranty as it controls the flow the same as a tap or a thermostatic shower.
      The CombiSave has won several awards including The UK innovation award for customer benefit.
      And you don’t seam to understand “ECO MODE”! When ECO Mode is lite, the boiler does not fire up, so you wait up to a minute for the water to get hot.
      When ECO mode is not illuminated the the boiler does fire up frequently using put o £200 of wasted gas. The manufactures can do this as this process is not measured in their efficiency testing. A bit like Volkswagen!

  • Kp January 24, 2018, 1:13 am

    Except none of it is “wasted” or indeed saved is it?
    Most of the energy will go into heating up the ambient temperature of the house…


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