West London Gas Safety Check and CP12 Landlord Guide

A gas safety check and a boiler service are two different jobs. Mixing them up is the most common mistake landlords and homeowners make before the heating season.

CP12, boiler service or visual check?

These three get confused all the time, and the difference matters. A Landlord Gas Safety Record (CP12) is a legal safety inspection under Regulation 36 of the Gas Safety (Installation and Use) Regulations 1998. It checks that appliances and flues are safe. It says nothing about how well the boiler runs.

A boiler service is maintenance to the manufacturer’s schedule. It cleans components and keeps the boiler efficient. A service on its own does not give a landlord a certificate.

A visual check is you looking at the flame and the flue terminal. It is useful between visits. It never replaces an engineer.

Booking the CP12 and a boiler service together saves money. It also protects your warranty, because most manufacturers expect a service every year.

What the engineer tests on site, in order

A CP12 visit takes 30 to 45 minutes for a typical home. This is the order we work in.

1. Gas tightness test. We fit a gauge at the meter and run a pressure drop test lasting about two minutes. A steady reading means the pipework is sound. A drop means a leak somewhere between the meter and the appliances.
2. Working inlet and burner pressure. We run each appliance and read the gas pressure arriving under load. Low pressure starves a burner and leads to poor combustion.
3. Flue gas combustion analysis. A calibrated electronic analyser measures carbon monoxide and carbon dioxide in the exhaust. The ratio must be below 0.0040. Anything higher means the appliance is not burning cleanly.
4. Flame supervision devices. On gas hobs and ovens we light the burner, put the flame out and time the cut-off. A working thermocouple shuts the gas within about 60 to 90 seconds. A slow or failed cut-off is a defect.
5. Ventilation and flue siting. We check the flue terminal clearance from openable windows and vents. We also confirm any required air vent is open.
6. The record. We write up every appliance, every reading and any defects on the CP12.

These are checks, not repairs. If something fails, we explain what and quote a fixed price before any work starts.

What a CP12 costs in West London

Prices are fixed and quoted upfront.

The Homeowner Plan suits owner-occupiers who want the standard annual service and priority booking spread over the year.

Renew early without losing your date

Think of it like an MOT. Since the 2018 amendment, you can have the check done up to two months before the current certificate expires. Your renewal date does not move.

Say your certificate expires on 30 November. A check on 5 October still renews you to 30 November the following year. Book it earlier than two months and the new check date becomes your anniversary instead.

This makes tenancy changes easier. You can book a slot when access is convenient and still keep your annual cycle.

What the warning notices mean

If an appliance fails, the engineer gives the fault one of three classes. The Gas Safe Register uses the same system across the industry.

• Immediately Dangerous (ID). A threat to life. We disconnect or cap the appliance with your permission. It stays off until repaired.
• At Risk (AR). A fault that could become dangerous. We turn the appliance off with your permission.
• Not to Current Standards (NCS). Safe to use, but it does not meet today’s installation codes. It is advice and not a failure.

Fix ID and AR faults before anyone uses the appliance again. For a leak or a breakdown on the day, our emergency boiler repair service can quote the fix on the spot.

Landlord duties after the check

The check is only half the job. The paperwork has deadlines.

• Give existing tenants a copy within 28 days of the check.
• Give new tenants a copy before they move in.
• Keep each record for at least two years.

A letting agent can handle copies for you. The record must carry the agent’s or landlord’s name and address. The HSE record-keeping guidance sets out what the record must contain.

If a tenant will not give access

Do not force entry. You must show you took reasonable steps. Leave a notice after every missed visit. Write to the tenant and explain the check is a legal requirement for their safety. Keep copies of everything. Start inside the two-month window so there is time to rearrange.

We carry out CP12 visits for landlords in Hammersmith, Fulham, Harrow, Acton and Queen’s Park. Our landlord gas safety certificate page has the full process.

Carbon monoxide alarms in rented homes

Landlords have a separate duty. Under the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, a working CO alarm is needed in every room with a fixed combustion appliance. Gas cookers are not counted. You must repair or replace an alarm once you are told it is faulty.

Test every alarm monthly. The test button only proves the battery and sounder work. It does not test the sensor. Read the replace-by date printed on the casing and swap the unit when it passes.

NHS guidance lists the symptoms. Headaches and dizziness that ease when you leave the house are the biggest clue.

What you can check yourself

The law draws a clear line. Only a Gas Safe registered engineer can work on a gas appliance.

Stop and call a Gas Safe engineer if

• The flame burns yellow or orange. It is not getting enough air and is producing carbon monoxide.
• You see soot or brown-black marks around a boiler, fire or cooker. That points to incomplete combustion.
• A pilot light keeps going out.
• Windows in the appliance room mist up heavily. The flue may be blocked.
• Anyone has headaches that ease away from home and return in the evening.

These all mean the appliance is not burning safely. Carbon monoxide has no colour or smell, so guessing is a risk.

If you smell gas

Call the National Gas Emergency Service on 0800 111 999 first. Then do the following.

1. Open the doors and windows.
2. Turn the gas off at the emergency control valve by the meter, if you can reach it safely.
3. Put out naked flames and do not smoke.
4. Do not touch light switches or use anything electrical.
5. Get everyone out of the property.

Do not turn the gas back on until a Gas Safe engineer says it is safe.

Mistaken for something else

• Flu. Carbon monoxide poisoning feels like a virus. Flu does not ease when you go out for a few hours.
• A service reminder. A boiler service date is not your CP12 expiry. Check the date on the certificate itself.
• An engineer who is “Gas Safe”. Registration is by appliance type. Check the back of their ID card for the categories they can work on.

Frequently asked questions

What does an engineer check on a CP12?

A CP12 covers every gas appliance you provide, plus its flue and pipework. The engineer runs a gas tightness test, checks working pressure, analyses flue gases on boilers, tests flame failure devices on hobs and ovens, and checks ventilation and flue siting. Any defects are classed and written on the Landlord Gas Safety Record. A typical visit takes 30 to 45 minutes.

Is a CP12 the same as a boiler service?

No. A CP12 is a legal safety inspection. It confirms appliances and flues are safe to use, and it does not clean or tune anything. A boiler service is maintenance to the manufacturer’s schedule, and it keeps the boiler efficient and the warranty valid. We can do both in one visit for £170, instead of £79 and £120 booked separately.

How far in advance can I renew my gas safety certificate?

Up to two months before the current certificate expires. A check done in that window keeps your original expiry date, so your 12-month cycle does not shift. This came in with the 2018 amendment to the Gas Safety (Installation and Use) Regulations. Book earlier than two months and the new check date becomes your renewal date instead.

What happens if my tenant refuses access for the gas check?

You must show you took reasonable steps. Leave a notice after each missed visit, write to the tenant explaining the check is a legal requirement for their safety, and keep copies of everything. You cannot force entry. Inspectors look for repeated, documented attempts, so start well inside the two-month window to leave room to rearrange.

What does Immediately Dangerous mean on a gas safety record?

Immediately Dangerous means the appliance poses an immediate threat to life. The engineer disconnects or caps it with your permission, and it stays off until a Gas Safe engineer has repaired it. If a repair is possible on the visit, we give you a fixed price before any work starts. At Risk faults are switched off with permission too.

Are gas cookers checked as part of a CP12?

Yes. Gas hobs, ovens and cookers you supply are part of the check. The engineer tests the flame supervision device by putting out the flame and timing the gas cut-off, which should happen within about 60 to 90 seconds. Appliances your tenant owns are not your legal duty, but the pipework and flue serving them are, and we check those.

Who gets a copy of the gas safety certificate?

Existing tenants get a copy within 28 days of the check. New tenants get one before they move in. You keep your own copy for at least two years. A letting agent can pass copies on for you. Electronic copies are fine if the tenant agrees, and the tenant can still ask for paper.

How much does a CP12 cost in West London?

Our CP12 is £79 fixed for 1 gas appliance, and each additional appliance is £35, so a boiler and a gas hob is £114. Landlords with a boiler due a service pay £170 for the combined visit. Prices are fixed and quoted before we start. Any repair found on the day gets its own fixed quote before work begins.

What happens next

Pick a morning (08:00 to 12:00) or afternoon (12:00 to 18:00) window online. The engineer runs the tests, and the Landlord Gas Safety Record follows once the visit is done.

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Related reading

• Landlord gas safety certificate (CP12)
• Boiler servicing
• Homeowner Plan
• Landlord gas safety certificate (CP12) guide
• How often should you service your boiler?

Landlord duties from the HSE landlord gas safety guidance. Carbon monoxide alarm rules from the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 on GOV.UK. Warning notice classes from the Gas Safe Register. Last reviewed October 2026. This guide is general safety advice and does not replace an inspection by a Gas Safe registered engineer.