Most Glasgow homes heat water in one of three ways: a combi boiler heating on demand, a system or conventional boiler feeding a hot water cylinder, or a standalone electric water heater. Which one you have decides what can go wrong and what a repair costs. A diagnostic visit is £70 to £110, common repairs run £120 to £400, and full replacement ranges from £650 for a vented cylinder to £3,200 for a new combi.
If you are not sure what you have, this guide will tell you — and then tell you whether repair or replacement is the sensible call.
How to Identify Your System
Combi boiler
One wall-mounted unit, no cylinder anywhere, no tanks in the loft. Hot water comes on demand when you open a tap. If you run out of hot water only when two showers run at once, this is what you have.
System boiler with unvented cylinder
A boiler plus a tall insulated cylinder, usually white metal, with a pressure relief pipe running outside and a small red expansion vessel nearby. No tanks in the loft. Common in newer homes across East Kilbride and other modern estates.
Conventional boiler with vented cylinder
A boiler, a copper or foam-lagged cylinder in an airing cupboard, and one or two tanks in the loft. Standard in older tenements, sandstone terraces and pre-1990s housing.
Electric water heaters
Either an immersion element in a cylinder, or a small point-of-use unit above a sink. Common in flats with no gas supply and in extensions.
Common Faults by System Type
| Symptom | Likely cause |
|---|---|
| Heating works, no hot water (combi) | Diverter valve or flow sensor |
| Hot water lukewarm only | Scaled plate heat exchanger, or cylinder thermostat set low |
| Hot water runs hot then cold | Failing flow switch, low flow rate, or blocked filter |
| No hot water at all, cylinder system | Motorised valve, cylinder thermostat or immersion failure |
| Water pressure dropping at boiler | Leak, or failed expansion vessel |
| Discharge pipe outside dripping | Unvented cylinder safety valve or expansion vessel fault |
| Banging or kettling noises | Scale or sludge in the heat exchanger |
Water Heater Repair and Replacement Costs (2026)
| Job | Typical Glasgow price (2026) |
|---|---|
| Diagnostic call-out | £70 – £110 |
| Diverter valve replacement | £220 – £400 |
| Plate heat exchanger replacement | £250 – £450 |
| Motorised valve replacement | £180 – £320 |
| Cylinder thermostat or immersion element | £120 – £280 |
| Expansion vessel replacement | £180 – £350 |
| Vented cylinder replacement | £650 – £1,100 |
| Unvented cylinder replacement | £1,400 – £2,600 |
| New combi boiler (like for like) | £1,900 – £3,200 |
Repair or Replace?
- Repair when the appliance is under about ten years old, parts are still available, and the quoted repair is well under half the replacement cost.
- Replace when the unit is over twelve to fifteen years old, has needed two or more repairs in a year, or parts are obsolete.
- Rethink the system if the household has changed — a family of five sharing one bathroom on a small combi will keep running out of hot water no matter how many parts you fit. That is a sizing problem, not a fault.
Efficiency is worth weighing too. The Energy Saving Trust publishes current running-cost comparisons between gas and electric water heating, and the gap is wide enough that relying on an immersion long-term rarely makes sense where gas is available.
Maintenance That Actually Extends Life
- Annual service. The most effective single thing you can do — combustion, pressures and safety devices all checked and recorded.
- Magnetic filter. Catches magnetite before it reaches the heat exchanger. Retrofitting one to an older system is cheap insurance.
- Correct system pressure. Keep a sealed system at 1.0 to 1.5 bar cold; constant topping up means a leak or a failed vessel.
- Cylinder temperature at 60°C. Hot enough to control legionella, not so hot that it scales the coil.
- Unvented cylinder service every year. A legal requirement in practice, and the valves genuinely do fail.
Glasgow-Specific Considerations
Soft water works in your favour here — scale failure is far less common than in hard water areas, so a lukewarm shower in Glasgow is more often a diverter valve or a flow issue than limescale. What does bite is system sludge in old steel and iron pipework, particularly in tenements and pre-war housing across the Southside, Paisley and Rutherglen. It blocks heat exchangers, kills pumps and leaves radiators cold at the bottom.
Water pressure is the other local issue. Upper-floor tenement flats on gravity-fed systems often have poor flow, which limits what a combi can deliver. That is worth establishing before anyone quotes a combi conversion — a flow test takes two minutes and prevents an expensive disappointment. Our emergency plumber cover handles no-hot-water calls seven days a week, and our central heating team handles the wider system.
Why Choose a Gas Safe Certified Engineer?
Any work on a gas water heater or boiler is legally restricted to a registered engineer, and unvented cylinders additionally require a G3 qualification. That combination matters, because hot water faults sit right on the boundary between the two. Precision Renovators hold both, so one visit covers the whole system rather than two half-diagnoses. Check any card on the Gas Safe Register, and see our plumbing and heating services or boiler installation pages for the full picture.
You may also like our guides on signs your boiler needs replacing and water pressure problems.
Frequently Asked Questions
Why do I have heating but no hot water?
On a combi it is usually the diverter valve or flow sensor. On a cylinder system it is more often a motorised valve, cylinder thermostat or immersion fault. Tell us which system you have and we will bring the right parts.
How long does a hot water cylinder last?
A vented copper cylinder often lasts 20 to 25 years; an unvented cylinder typically 15 to 20 with annual servicing. Weeping at a boss or the safety valve discharging regularly are end-of-life signs.
What temperature should my cylinder be set to?
60°C at the cylinder thermostat. Lower risks legionella, higher wastes energy and increases scald risk at the tap.
Why is water coming from the pipe outside?
On an unvented cylinder, discharge from the tundish pipe means a safety valve or expansion vessel fault. It is not normal and needs attention — the system is relieving pressure it should not be building.
Is it worth switching from a cylinder to a combi?
Sometimes. It frees a cupboard and simplifies the system, but only if incoming flow rate is good and the household is not running two showers at once. We flow test before advising.
How quickly can you attend a no-hot-water call?
Same day across Glasgow and the surrounding towns in most cases, with out-of-hours cover for genuine emergencies.
Ready to Get Started?
Precision Renovators are Gas Safe certified plumbing and heating engineers covering Glasgow and the surrounding towns. We diagnose the whole hot water system before quoting, give a fixed written price, and say plainly when replacement beats another repair. Browse our services or see our projects.
Get a Free Quote — or call and WhatsApp us on 07495 816227.
