Signed, Sealed, Delivered? A Glow-worm Boiler Quote Audit for 2026
Boiler quotes are odd documents. Two installers can visit the same house, recommend the same Glow-worm boiler and hand over paperwork that differs by thousands of pounds. One is itemised down to the last radiator valve; the other is a single number on a compliments slip.
The gap is rarely about the boiler itself. It is about everything wrapped around it — the flush, the filter, the controls, the paperwork, the bits nobody mentions until they are already in your airing cupboard. So before you sign anything in 2026, put these twelve questions to every installer who quotes.
1. How was the boiler size calculated?
Ask whether they did a room-by-room heat loss calculation or reached for the old bedrooms-and-bathrooms rule of thumb. It matters. An oversized Glow-worm will cycle on and off, waste gas and feel less comfortable; an undersized one will sulk through the coldest week of January. If the number appeared from nowhere, ask to see the calculation.
2. Which Glow-worm model is it, and why that one?
The range spans combis, system boilers and regular boilers at several price points, with different warranties and efficiencies. A decent quote names the exact model and explains the reasoning — hot water demand, flue route, space, budget. A quote that just says Glow-worm combi is not a quote; it is a guess.
3. Combi, system or regular — and does my home actually suit it?
This is not a lifestyle question. It comes down to mains flow rate, how many bathrooms are in use at once, whether you have space for a cylinder and how much hot water you genuinely draw. A good installer will test the flow rate rather than assume.
4. What does the warranty cover, and who registers it?
Glow-worm warranties often run to ten years, with longer terms on some models when fitted by an accredited installer. Ask what is covered, what is excluded and who submits the registration. It is normally the installer's job, and it needs doing promptly with the paperwork handed to you. Keep it somewhere safer than the boiler manual drawer.
5. Will the system be flushed, and to what standard?
A new boiler bolted onto a sludged-up system is a warranty claim waiting to happen. Ask whether the flush follows BS 7593, whether it is a chemical flush or a power flush, what inhibitor goes in and whether the water is tested afterwards. If flushing is not mentioned in the quote, it is either missing or buried.
6. Is a magnetic filter included in the price?
Many Glow-worm warranties expect one, and your heat exchanger will thank you. Ask which filter, where it will be fitted and whether it is a line item or an afterthought. A filter left off a cheap quote is one of the most common hidden extras.
7. What controls am I getting?
A boiler is only as good as the controls telling it what to do. Check whether the quote includes a programmer, room thermostat, smart control, weather compensation and thermostatic radiator valves. Ask who commissions the controls and explains them to you. A wall-mounted box you cannot work is not a control system.
8. Is commissioning paperwork part of the price?
The Benchmark checklist, flue gas analysis, gas rate check, standing pressure and a proper handover should all be included. These are not extras; they are the evidence that the installation was done correctly. An installer who treats paperwork as optional is telling you something.
9. Who notifies Building Control?
In England and Wales, notifiable boiler work is usually handled through a Competent Person Scheme, with a certificate arriving afterwards. Ask who is responsible and when you should expect it. You will want that certificate if you ever sell the house.
10. What about the flue, condensate and making good?
Flue route, plume kit, condensate pump or soakaway, boxing-in, brickwork, scaffolding — these are where budgets quietly unravel. A thorough quote accounts for them. A cheap one assumes the flue will go straight out of the wall in the most convenient possible place.
11. Which extras are optional and which are essential?
Gas run upgrades, an electrical spur, new radiator valves, a cylinder, relocating the boiler — some are genuinely necessary, others are nice-to-haves. Ask for an itemised list of optional works with prices, so you can decide rather than discover.
12. What happens if something goes wrong next winter?
Ask about call-back times, the labour warranty, whether servicing is included and who answers the phone in February. Get it in writing. The cheapest quote in October can become the most expensive relationship of your year.
The quote you can trust
A fair quote is not the cheapest quote. It is the one that shows its workings — sizing, model, flush, filter, controls, paperwork and aftercare — without you having to drag each item out of the installer.
If a quote arrives without a site visit, without a heat loss calculation, without a Gas Safe number or with a suspiciously large deposit request, treat it as a warning rather than a bargain. Get three quotes, compare them line by line and ask the awkward questions now. It is far easier than asking them in the middle of a cold snap.
