If your boiler is over 12 years old, making strange noises, or your heating bills have crept up noticeably, you're probably weighing up whether to repair or replace it. This guide will help you make the right call — and if you do decide to replace, explain exactly what you should be looking for.
Repair or Replace?
The rule of thumb most heating engineers use is this: if the repair cost is more than half the cost of a new boiler, replace it.
But there are other factors:
Replace if any of these apply:
- The boiler is more than 12–15 years old
- It needs a repair costing over £500
- You're having to repair it annually
- Parts are becoming hard to source (common with older Baxi, Glow-worm, and older Worcester Bosch models)
- Your heating bills have been rising steadily without explanation
Repair if:
- The boiler is under 8 years old and has a minor fault
- It's still under manufacturer warranty
- The repair is straightforward (ignition, diverter valve, thermostat) and under £300
Which Type of Boiler?
There are three types: combi, system, and heat-only (also called regular or conventional). Understanding which suits your home is the most important decision.
Combi Boiler
A combi (combination) boiler heats water on demand — there's no hot water cylinder or cold water tank in the loft. When you turn on a tap, the boiler fires up and heats water directly.
Best for: Flats, small to medium houses (up to 3 bedrooms), homes with one bathroom, properties where loft or cupboard space is limited.
Advantages:
- No hot water cylinder takes up airing cupboard space
- Hot water is unlimited (you won't "run out")
- Simpler installation, lower cost
Disadvantages:
- Flow rate is lower than a cylinder — running two showers simultaneously can be problematic
- Not ideal for homes with multiple bathrooms in constant use
System Boiler
A system boiler heats water and stores it in a separate hot water cylinder. The cylinder is pressurised (unlike old vented cylinders), which gives good flow rates.
Best for: Medium to large houses with multiple bathrooms, families who use hot water simultaneously.
Advantages:
- Multiple taps/showers can run at full pressure simultaneously
- Faster hot water delivery (stored, not on-demand)
- Compatible with solar thermal top-up if you're planning ahead
Disadvantages:
- You need space for a cylinder (typically an airing cupboard)
- If you run out of stored hot water, you wait for it to reheat (usually 20–30 minutes)
Heat-Only (Regular) Boiler
A heat-only boiler works with both a hot water cylinder and a cold water storage tank in the loft. This is the old-fashioned setup found in most homes built before the 1990s.
Best for: Older properties that already have this setup, homes with multiple bathrooms and high hot water demand.
Advantages:
- Handles very high simultaneous demand well
- Compatible with older radiator systems designed for low pressure
Disadvantages:
- Takes up significant space (cylinder + loft tank)
- Open-vented system means lower water pressure
Most of the time, if you're replacing a heat-only system, we'll convert it to either a combi or a system boiler — the running costs are lower and the performance is better.
Which Brand?
Worcester Bosch
The most commonly recommended brand by Gas Safe engineers in the UK, and for good reason. Worcester Bosch boilers are reliable, efficient, and well-supported. Their Greenstar range is the most popular in the country.
Manufacturer guarantee: up to 12 years (8 years standard, up to 12 with registered installer using genuine parts).
Best models: Greenstar 4000 (combi), Greenstar 8000 (high-output combi/system).
Vaillant
German engineering, strong reliability record, slightly more repairable than Worcester Bosch in some engineers' experience. The ecoTEC range is their workhorse.
Manufacturer guarantee: up to 10 years.
Best models: ecoTEC Plus, ecoTEC Pro.
Ideal
A UK manufacturer with a good mid-range reputation. Ideal boilers tend to be competitively priced without significant quality compromise.
Manufacturer guarantee: 7–10 years depending on model.
Best models: Logic Max, Vogue Max.
Brands to Be Cautious About
Combi boilers from less well-known brands (some imported budget brands) can be hard to get parts for within 5–7 years. We only install from brands where we're confident parts will be available for the life of the boiler.
Efficiency: What the Numbers Mean
All new boilers sold in the UK must be A-rated for energy efficiency, meaning they convert at least 90% of the gas they burn into heat. The best achieve 94–98% efficiency.
The old G-rated boilers (common before 2004) might be as low as 60–70% efficient — meaning 30–40p in every pound you spend on gas is wasted up the flue.
Replacing a G-rated boiler with an A-rated one typically saves £200–£400 per year on gas bills for a typical Hertfordshire semi-detached. The payback period on the boiler cost is usually 5–8 years.
Hertfordshire-Specific Considerations
As we cover throughout this site, Hertfordshire's hard water (300–400ppm) accelerates scale buildup inside heat exchangers. When you get a new boiler fitted:
- Insist on a system flush before installation — installing a new boiler onto a sludgy old system is one of the most common causes of early boiler failure
- Fit a magnetic filter (e.g., Adey MagnaClean) — most manufacturers require this to validate the warranty
- Add a scale inhibitor to the system water — Fernox or similar
- Consider a water softener if you don't already have one — it's the most comprehensive long-term protection
What Does a New Boiler Cost?
Prices vary based on boiler model, system type, and installation complexity.
As a rough guide for Hertfordshire:
| Type | Boiler + Installation | |------|----------------------| | Combi (like-for-like swap) | £2,000–£2,800 | | Combi (conversion from heat-only) | £2,500–£3,500 | | System boiler + new cylinder | £3,000–£4,500 | | Heat-only (like-for-like) | £2,200–£3,000 |
These figures include supply, installation, flue, filter, inhibitor, Gas Safe certificate and commissioning. They don't include optional extras like a new smart thermostat, which typically adds £150–£300 fitted.
Be cautious of quotes significantly below these ranges — they often involve cheaper boiler models with shorter guarantees, or cuts to system preparation (like skipping the flush) that will cause problems later.
Ready to Get a Quote?
We install Worcester Bosch, Vaillant, and Ideal boilers across all of Hertfordshire. All installations are carried out by Gas Safe registered engineers and include a full system flush, filter, inhibitor, and commissioning.
Contact us for a free, no-obligation quote, or call us directly on 0208 092 1359. We're usually able to visit within 24–48 hours.