The short version
- A straight combi-for-combi swap is the cheapest job on the list because pipework barely moves
- Converting from a cylinder system to a combi costs more — you're removing tanks and re-running pipework
- Warranty length is usually the biggest difference between two quotes for 'the same' boiler
- Fixed written quotes should list the appliance model, flue, filter, controls and making good
What actually sits inside the price
Every compliant install includes more than the boiler itself. When you compare quotes, check that all of the following are included rather than added later.
- The appliance and its flue kit, sized for your property
- System filter and chemical inhibitor (required by most manufacturer warranties)
- Controls — a programmer or smart thermostat where the old one won't carry over
- Gas soundness testing, flue gas analysis and Building Regulations notification
- Removal and safe disposal of the old appliance
Why two quotes for the same boiler differ
The appliance is often the smallest variable. Registered installers get different warranty tiers from manufacturers, and a longer warranty usually means a slightly higher price and a stricter install spec. A quote that skips a filter or a chemical flush is cheaper on the day and expensive later, because it can invalidate the guarantee at the first claim.
The property factors that move the number
In practice, the biggest cost jumps come from the house rather than the boiler.
- Moving the boiler to a different wall or room
- Going from a vented cylinder system to a combi
- Long or awkward flue runs, especially in mid-terraces
- Upgrading the gas supply pipe where the existing run is undersized
- A heavily sludged system that needs a power flush before the new boiler goes on
How to compare quotes without getting caught out
Ask each installer for the model number, the warranty length in writing, and whether the price includes making good. Then compare like with like. If one quote is dramatically lower, the difference is almost always in the warranty tier, the filter, or the flushing method.
Common questions
Do you charge for a quote?+
No. We survey, discuss options and send a fixed written quote at no cost.
Is finance available?+
Ask when we quote — we'll talk through the options that apply to your job rather than guess up front.
Can you fit the boiler in one day?+
A like-for-like combi swap is usually a single day. Conversions from a cylinder system often run into a second day.
Does the price change once you start?+
Only if we find something hidden that we couldn't see at survey — and we'd talk to you before doing anything chargeable.
Get a fixed written boiler quote
No pressure, no sales visit theatre — a survey, your options and a price in writing.