Boiler replacement: delight or disaster? – a case example

“The boiler’s broken down” and immediately we have a tricky and potentially expensive problem. Of course to add to my pain, it is late autumn and we need the heating to work again fast.

One may need only to change a boiler once in a lifetime but when it happens what do we do to get a new boiler installed with the minimum of fuss and at a reasonable price? This blog suggests an approach, based upon my recent experiences of boiler installations:

There are three key steps, in my view to replacing a boiler :-

1. Obtain several plumber recommendations and quotes
2.  Agree the price and installation scope
3. Complete and register the work

Our existing domestic gas heating system comprises two zones (ground and first floor) (Good), but with two Potterton Suprima 100 boilers; one on each zone (Bad). The problems with our existing system (purchased with the house) included excessive on / off cycling due to the boilers being grossly oversized against system load, a resulting low boiler efficiency and high gas consumption. The electronics on one of the boilers failed prompting the opportunity for a permanent solution. There is little point throwing good money after an old boiler, so we decided to replace them with a modern arrangement.

Step 1:

It is advisable to write a one page summary of all the things you want the plumber to do (the work). Nowadays it is possible to do your research on line.

The solution was to strip out both boilers and install a single boiler with three zones; Ground, First and Hot Water. I calculated the expected combined heating and hot water load and then selected a boiler. I chose a Vaillant Condensing Ecotech plus 624 (heat output 8.7 to 24kW modulating) as a preferred option to discuss with the plumber. Vaillant in my view is a good brand, but you can check all boilers and their efficiencies at independent site SEDBUK.You might choose to find an independent professional to help you with this selection, for the reason I outline below.

The important point is to choose a qualified gas safe plumber. You should check their registration with gas safe. Remember that the boiler should be registered at completion with gas safe and with the manufacturer for a valid warranty. The new boiler also needs to be serviced each year to retain its warranty.

You should obtain at least two quotes. I used WhichLocal to find local recommended plumbers. This is not intended as a plug for Which? but I have used their trades recommendation service for several years now and whilst you have to pay a monthly subscription it is much better in my experience than randomly using the phone book.

Step 2:

I approached four plumbers, including British Gas, expecting not all to want to quote. They all visited the house and quoted against the same written summary. This is important as you need to feel comfortable with the actual person who will do your work. Asked to size the boiler, they all selected boilers one or two sizes higher than my calculation suggested. I gave them the heat loss figures in the summary. 

One, an eco-plumber, told me that he could calculate the most eco-efficient boiler size. He would not let me see his calculations but selected a boiler two sizes larger. The main point about a condensing boiler is that it should be worked hard with lower return temperatures to maximise its operation in condensing mode when it is most efficient. An oversized boiler will cycle more and condense less of the time. So not only is the boiler more expensive but you will end up with a higher than expected running cost. I gave him my calculations and asked him to tell me where our figures differed. He did not come back!

I ended up with three quotes. These ranged from £2,700 to over £4,000 (ex. VAT). The lowest quote did not include all the items in my summary and was vaguely worded. It was not easy to clarify the items clearly with the plumber, with a real risk of extra items being added during the works. So I discarded this quote. The next lowest was just over £3,000. We discussed the unclear points, agreed a scope and finalised the price at £3,013.20 (ex. VAT). During our discussion, it was clear that the plumber would do the work well.

You should also confirm upfront with your chosen plumber his day-rate to cover any unforeseen extra work and the number of days to do the work.

Trade suppliers are no longer discounting better than online retailers. So I agreed with the plumber to buy the agreed boiler kit separately (£1,084) online. 

Step 3:

Pushing all the discussions upfront, meant that we both had a clear and common idea of the work as it started. Most of the pipework and units had to be stripped out and re-plumbed during the work to achieve a better maintenance layout.

The plumber managed to get the hot water restarted on an immersion within a day, whilst the whole work took four days. Pipework was insulated and labelled. The only unforeseen item was the vertical flue clashing with an uncovered roof joist. We repositioned the joist to avoid flue bends using the agreed daywork rate.

My conclusions are:

• Use your time upfront to do steps 1 and 2 well and then you will likely have a smoother step 3 with someone that you can trust;
• Plan and document the work requirement. Use a recommendation service and get several quotes. Take time to get the plumbers’ advice but also use your own independent judgement as to what is right for you;
• Discard anyone who you are not sure about – find more quotes if you need to;
• The cheapest quote is unlikely to be the best considered quote, leading to potential problems and additions;
• Document your agreement clearly and shop around for the best online boiler price; it may be cheaper than the plumber’s trade price;
• Allow the plumber to make a reasonable profit and you will likely get a ‘win-win’ outcome;
• Remember to register the work; especially if you own and may sell your house soon.

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