Unvented Cylinder Servicing & Repairs
Is your unvented hot water cylinder losing pressure, not heating properly, or overheating? AG Heating Ltd provides expert unvented cylinder servicing, fault diagnosis, and repairs across London and Hertfordshire. Gas Safe registered and fully insured.
5★ reviews
By our customers
Across London, Hertfordshire & beyond
10+ years
Of Experience
Years of gas and heating expertise
Gas Safe
Registered & Fully Insured
Registration #973229
24/7
Emergency Callouts
Always available when you need us
Professional Unvented Cylinder Servicing
Unvented Cylinder Servicing
Whether your unvented cylinder is due its annual service, showing signs of reduced performance, or you’ve had no hot water at all, AG Heating Ltd provides a thorough, professional service. Our G3-qualified engineer will inspect every critical component, test all safety devices, and leave your system working safely and efficiently — giving you full peace of mind.
A standard unvented cylinder service includes:
- Full visual inspection of the cylinder, pipework, and connections
- Pressure relief valve (PRV) check and test — replaced if faulty or overdue
- Expansion vessel pre-charge pressure check and recharge or replacement as needed
- Thermostat and temperature and pressure (T&P) relief valve testing
- Safety device testing including high-limit thermostats and motorised valves
- System pressure check and adjustment to manufacturer specification
- Legionella risk check and temperature verification
- Full service report provided on completion
Most unvented cylinder services are completed within two to three hours. Our G3-qualified engineer will confirm the expected duration and provide a clear fixed price before any work begins.
Does Your Unvented Cylinder Need Attention?
A service, repair, or inspection is worth arranging when one or more of the following apply:
✅ No hot water or water that never reaches the right temperature
✅ Loss of pressure — cylinder repeatedly drops below operating pressure
✅ Overheating — water from the hot tap is scalding or much hotter than set
✅ Pressure relief valve dripping or discharging water into the tundish
✅ Cylinder is over 10 years old and has never been professionally serviced
✅ Strange noises — banging, hissing, or rumbling from the cylinder
Not every fault requires a full replacement. Where a repair or component swap is all that’s needed, we’ll tell you clearly and carry it out at a fair, fixed price — no unnecessary upselling.
Common Signs Your Unvented Cylinder Needs Servicing
These are the most common symptoms our customers report before calling us for an unvented cylinder service or repair:
- No hot water or intermittent hot water supply
- Pressure relief valve dripping continuously or discharging into the tundish
- Water overheating — scalding temperatures from the hot tap
- Cylinder losing pressure repeatedly despite being topped up
- Banging, hissing, or rumbling noises from the cylinder or pipework
- Visible leaks from the cylinder body, valves, or surrounding pipework
- Cylinder has not been serviced in over 12 months — manufacturer and warranty requirement
If you’re experiencing any of these issues, call us and we’ll diagnose and resolve the fault quickly — with 24/7 availability for emergencies.
What to Expect from Our Cylinder Service
We keep every cylinder job straightforward and stress-free from first contact to completion:
- Call or message us — we respond promptly, day or night
- We discuss your cylinder, its symptoms, and service history to confirm the best course of action
- We agree a convenient date and provide a clear, fixed price — no surprises
- Our G3-qualified engineer arrives fully equipped with all required test equipment and spare components
- The cylinder service or repair is carried out thoroughly, safely, and to manufacturer specification
- All safety devices are tested and confirmed in working order before we leave
- A full service report is provided and everything is explained clearly
No jargon. No hidden costs. Just professional unvented cylinder servicing you can rely on.
Why Choose AG Heating for Unvented Cylinder Servicing?
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Gas Safe Registered
All installations and repairs are carried out by a Gas Safe registered engineer. Your safety and legal compliance are guaranteed — every time.
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Transparent Pricing
We quote clearly before we start. What we say it’ll cost is what you pay — no hidden charges, no last-minute extras.
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G3 Qualified Engineers
Unvented cylinders must legally be serviced by a G3-qualified engineer. All our engineers hold the required G3 certification, so every service is fully compliant, safe, and backed by professional expertise.
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Honest Advice
If a repair is all you need, we’ll say so. We recommend what’s right for your home — not what earns us the most.
Unvented Cylinders — Frequently Asked Questions
How often should an unvented cylinder be serviced?
Unvented cylinders should be serviced every 12 months. Annual servicing is a requirement of most manufacturer warranties and is strongly recommended by the Benchmark scheme. Regular servicing keeps all safety devices in working order, maintains efficiency, and protects your warranty.
How much does an unvented cylinder service cost?
Cost depends on the cylinder type, its age, and the work required. We provide a clear, fixed quote before any work begins — so you know exactly what you’re paying. No hidden charges and no last-minute extras.
My cylinder is losing pressure — what does that mean?
Pressure loss in an unvented cylinder is usually caused by a faulty or weeping pressure relief valve, a failed expansion vessel, or a leak in the system pipework. It should not be ignored — low pressure affects performance and, in some cases, can indicate a safety issue. Call us and we’ll diagnose the cause and fix it promptly.
The pressure relief valve is dripping — is that dangerous?
A dripping pressure relief valve is a warning sign that should be investigated urgently. It can indicate excessive system pressure, overheating, or a valve that has failed and needs replacing. Do not ignore it or cap it off — call AG Heating immediately and we’ll assess and resolve the issue safely.
Do I need a G3 engineer to service my unvented cylinder?
Yes — by law, work on unvented hot water systems must be carried out by a G3-qualified engineer. This is a legal requirement under Part G of the Building Regulations. All AG Heating engineers hold full G3 certification, ensuring every service is legally compliant and carried out to the highest safety standard.
Can you repair an unvented cylinder or does it need replacing?
In many cases, a cylinder can be repaired rather than replaced — for example, by replacing the expansion vessel, pressure relief valve, thermostat, or immersion heater element. We’ll always give you an honest assessment. If a repair is viable and cost-effective, we’ll recommend it. If replacement is the safer or more economical option, we’ll explain why clearly.
Do you cover emergency unvented cylinder repairs?
Yes — AG Heating provides 24/7 emergency callouts for unvented cylinder faults including no hot water, pressure loss, overheating, and pressure relief valve discharge. If your cylinder develops a fault, call us and we’ll get to you as quickly as possible, day or night, to restore your hot water and make the system safe.
Book an Unvented Cylinder Service Today
Whether your cylinder needs its annual service, a fault diagnosis, or an emergency repair — AG Heating Ltd is here to help. G3-qualified engineers, transparent pricing, and 24/7 availability.
☎ Call: 07400 400 430
✉️ Email: info@agheating.co.uk