i am contemplating an extension to the rear of my property. Unfortunatley the balanced flue from my 27 year old gas boiler is in the way. The obvious answer is to move the boiler and by far the easiest solution would be to install a combi boiler in the airing cupboard upstairs.
The house is a modern four bedroom house with two bathrooms and currently 11 rads.
I have been a little dubious about combi boilers in the past regarding their capacity to deliver a sufficiently fast rate of flow for the hot water but my installer assures me that a modern boiler will be fine. He suggest a 35 or 40KW model Although we have two showers I can't remember that these have ever been used simultaneously so I think that the flow rate shouldn't be a problem.
Only other problem I can think of is lack of back up in form of immersion heater for hot water but I can live with that.
Gas pipe will have to be rerouted externally as will need 22m or bigger and currently 15mm but even a straight replacement would necessitate this change
Any thoughts
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The thing round here these days seems to be somehow delivering your hot water at mains pressure, so no shower pump etc needed, and scalding at the tap happens even more quickly.. I guess it costs a few thou though.
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We have a 8KW electric power shower to one of our 2 bathrooms. It suffers from a real compromise - a barely adequate flow and a moderate temperature.
In winter when the water feed from the cold water tank is lower than summer, a barely adequate flow reduces to a dribble at aforesaid temperature. Alternative is full fow and luke warm.
Fortunately our en-suite power shower comes off the conventional hot water tank so it's not a major issue.
However if you enjoy hot (not tepid) full flow showers then a combi boiler even at the capacity you suggest may struggle if two showers or baths + heating is running at the same time.
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We have two in the place in England. The larger runs two showers, a bath and about 19 radiators. Mains pressure very hot water. (one needs cold water on as well). Radiators all capable of being very hot.
I think it switches from the heating when hot water is being drawn, though it's never been an issue.
Gas fired, love it. I can't think of a downside.
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40kW will do about 16 litres / min at 35C temp rise, which should be adequate...! It will probably need a 28mm gas supply all the way back to the meter, and it will need a condensate drain, so worth figuring out if either of those will cause a problem with the proposed location - and if it's not on outside wall, the flue extensions get horribly pricey (like more than the boiler!). The downsides are that you lose heating when the water is running (but that's not a huge issue unless you have teenagers that spend an hour in the shower!), and if the boiler is not running, it takes a while to make any hot water, so if it's a long run to the kitchen sink it can take an age just to draw up a bowl of water to wash up. They have a bit of a rep as unreliable, but they have got better these days, and if you treat them with a bit of care (only put a hot top on if actually want hot water, otherwise it cycles the boiler and 3-way valve unnecessarily) then you should get 10 years+. 27 as per you current one is unlikely....!
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Thanks. Only two in the house so I don’t think there is going to be any real conflict in demand for hot water. If my wife is in the shower she can’t be washing up! :-)
Boiler would be next to bathroom and directly above kitchen so pipe run would not be excessive. Boiler would be on outside wall so flue not a problem and gas pipe can be routed up outside wall and through gable end and into loft space. As regards reliability comes with 10 year warranty.
Longevity of boiler probably not an issue. I would say its chances of lasting 27 years would be massively higher than mine!
Only real issue then seem to be the cost. Quoted around £3,500
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>> Only real issue then seem to be the cost. Quoted around £3,500
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If it helps, I paid £2,200 to have a system boiler replaced a couple of months ago. I went for a Viessmann (10 year warranty) but it was a like-for-like replacement - no need to move the gas or water pipes. It might have needed a slightly different flue position - can’t remember. But it’s on an outside wall.
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Yes I had a similar quote to you for a like for like system oiler replacement last year. I will get another quote but I think £3,500 is probably a reasonable quote inv view of the work needed.
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If your radiators are 27 (or more) years old to get the 10yr warranty on the boiler will require a full system power flush. Check if this is included in the price - and then factor in the the leaks it exposes!
There was another thread on this recently.
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Yip, I think I mentioned the power flush requirement when I had my boiler replaced last spring. I don't recall any age qualification though. Luckily my next door neighbour is a plumber and I think the whole thing was only about £1800 incl new boiler and power flush - I may be a couple of thou out though. It was pretty much like for like but a new flue was required, and it wasn't a combi boiler!
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We have a 32kw combi installed 2yrs ago, replaced a 28yr old Mison Midas.
Heats 24'x14' room from 18c - 25c in about 1.50hrs, runs 7 rads, sizes vary from 5ft doubles to 3ft singles, runs a bath (hot tap only ) to overflow in 13mins, and runs a thermostatically-controlled shower (no -pump req) with a flow that you nearly drown under! (thermstatic showers are fed by both a hot and cold water supply, so double the water capacity delivery of an electric shower, as your probably aware of!) HTH ;-)
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and runs a thermostatically-controlled shower (no -pump req) with a flow that you
>> nearly drown under! (thermstatic showers are fed by both a hot and cold water supply,
>> so double the water capacity delivery of an electric shower, as your probably aware of!)
>> HTH ;-)
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Not really double the flow, since the hot water coming out of the boiler is only just above shower delivery temp, so the amount of cold mixing will be small. But you are staring off from a point of 32kW heat input rather than the paltry 8kW that the smallest electric showers make, which is only good for about 3 litres / min in the winter.
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Combi Boiler - smokie
