Nobody plans to replace a boiler. The decision usually arrives on a cold morning with an engineer standing in the kitchen quoting for a part. The honest answer is rarely obvious from the repair price alone, because the number that matters is not what this repair costs — it is what the next three years cost.
This guide sets out the way we assess it on site in Kelso, Melrose, Duns, Haddington and the surrounding villages, so you can make the same judgement rather than take a sales pitch on trust.
The four questions that settle most cases
- How old is the appliance? Under eight years, repair is almost always right. Over fifteen, replacement usually is. Between the two, the other three questions decide it.
- Are parts still supported? Once a manufacturer discontinues a heat exchanger or PCB for a model, the next failure may be unfixable at any price.
- How many faults in the last two years? One is bad luck. Three separate failures means the appliance is at the end of its service life, not suffering a single problem.
- What is the repair as a share of a replacement? A common working rule is that if a repair costs more than roughly a third of a new installation on an appliance over ten years old, replacement is the better use of the money.
Indicative repair costs versus replacement
The figures below are indicative ranges for this area, quoted to help you frame the decision rather than to price your job. Actual cost depends on the appliance, the part, access and whether the visit is an emergency callout.
| Work | Indicative range | Usually worth it? |
|---|---|---|
| Thermocouple, thermistor or sensor swap | £120 – £220 | Yes, at almost any age |
| Expansion vessel recharge or replacement | £150 – £300 | Yes, unless the boiler is 15+ |
| Diverter valve or valve cartridge | £250 – £450 | Yes under 10 years, marginal over 12 |
| Pump replacement | £250 – £420 | Yes under 12 years |
| Fan or gas valve | £350 – £600 | Marginal over 10 years |
| Printed circuit board (PCB) | £400 – £700 | Rarely, on an older appliance |
| Primary heat exchanger | £600 – £1,100 | Almost never, over 10 years |
| Combi boiler replacement, like-for-like | £2,200 – £3,600 | The benchmark to judge against |
| System conversion or relocation | £3,500 – £6,000+ | Where a swap is not possible |
Running cost is part of the sum
An old non-condensing or early condensing boiler running at poor seasonal efficiency wastes fuel every day it stays in service. On a Borders property with a long heating season and a draughty stone envelope, the difference between an appliance operating in the low seventies for efficiency and a modern condensing boiler correctly commissioned to condense properly is real money over a winter.
The catch is that many replacement boilers never achieve their rated figure because the flow temperature is set too high and the system never returns cool enough water to condense. If you replace, insist the installer commissions the flow temperature and controls properly — otherwise you have bought efficiency on paper only. Our guide to why boilers short-cycle covers the same ground from the fault side.
When to repair even on an old boiler
- It is mid-winter, the fault is cheap, and you need heat now — repair, then plan a replacement for spring when installers have availability and you are not deciding under pressure.
- You are selling within a year and the appliance is serviceable and safe.
- The property is a rental with a tenant in place and the repair restores compliant, safe operation. Note that a landlord's duty is safety, not modernity.
- The fault is external to the boiler — a seized zone valve, a failed thermostat, a sludged system. Replacing a boiler will not fix a system problem, and a new appliance dropped onto a dirty system will fail early.
When to stop repairing
- The engineer has condemned the appliance as immediately dangerous or at risk. That decision is not negotiable and the gas supply to it will be capped.
- The heat exchanger has failed on an appliance over ten years old.
- Parts are obsolete, or lead times run to weeks in the middle of the heating season.
- You have paid for three or more separate repairs in twenty-four months.
- The appliance is badly oversized for the property, so it short-cycles, wears fast and burns fuel that never reaches the rooms.
A word on the intermediate option
There is a middle path people forget: keep the appliance and fix the system around it. A power flush, a magnetic filter, correct inhibitor dosing, balanced radiators and a decent programmable control can transform a serviceable ten-year-old boiler that has been struggling against a dirty circuit. That package costs a fraction of a replacement and buys several years.
It only makes sense where the appliance itself is sound. Where it is not, cleaning the system is a sensible first step to be done as part of the replacement, not instead of it.
What we do on a decision visit
We test rather than guess. That means checking gas rate and combustion, testing the expansion vessel charge, reading fault history from the appliance where it stores it, checking system water condition, and confirming parts availability with the manufacturer before we recommend anything.
You then get both numbers in writing: what the repair costs, and what a replacement costs specified properly, so you can decide with the actual figures rather than an impression. If a repair is the right answer, we will say so — we would rather have the servicing relationship for the next decade than the one-off sale.
Frequently asked questions
- Is there a fixed age at which a boiler must be replaced?
- No. There is no legal age limit. A well-maintained appliance with available parts can run safely well past fifteen years. The trigger is safety, parts availability, repair frequency and running cost, not the date on the badge.
- Will a new boiler definitely cut my bills?
- It should, but only if it is correctly sized, correctly commissioned and running at a flow temperature low enough to condense. An oversized appliance set to a high flow temperature can perform little better than the boiler it replaced.
- My boiler was condemned. Do I have to replace it immediately?
- If it is classified immediately dangerous the gas supply to it will be disconnected and it cannot be used. At risk means it must not be used until repaired. Either way you need heat and hot water restored, and we prioritise those calls.
- Can you repair boilers you did not install?
- Yes. We service and repair all common gas and oil appliances across the Borders and East Lothian, whoever fitted them.
Get both numbers before you decide
We will diagnose the fault, confirm parts availability, and quote the repair and the replacement side by side so you can choose on facts.