If you let a property with a Vaillant boiler, an annual gas safety check is a legal duty, not a choice — and it’s what protects your tenants from gas leaks and carbon monoxide. This guide explains the gas safety certificate (CP12) as it applies to Vaillant boilers: what the law requires, how renewal works, the Vaillant fault codes landlords see most, and what you can safely check yourself versus what needs a Gas Safe registered engineer.
Last reviewed: 7 August 2026.
Safety note: only a Gas Safe registered engineer may work on the gas side of a boiler or issue a certificate — it is illegal for anyone else. The checks below are limited to safe, non-gas actions.
Key takeaways
- A gas safety certificate (CP12 / Landlord Gas Safety Record) is valid for 12 months and must be renewed annually by a Gas Safe registered engineer.
- Give tenants a copy within 28 days of the check, and to new tenants before they move in; keep records for at least two years.
- Breaches can mean a fine of up to £20,000 and/or imprisonment — an unlimited fine at the Crown Court.
- A CO alarm is required in any room with a fixed combustion appliance, including a gas boiler.
- Common Vaillant fault codes (F22, F28/F29, F75) usually point to pressure, ignition/gas, or the pump — some are safe DIY checks, others need an engineer.
What the gas safety certificate is
A gas safety certificate — the CP12, formally the Landlord Gas Safety Record — confirms that a Gas Safe registered engineer has checked the gas appliances, flues and pipework you provide and found them safe. It’s required under the Gas Safety (Installation and Use) Regulations 1998 for anyone letting on a tenancy of under seven years. For a Vaillant boiler, the engineer checks gas tightness, burner pressure and combustion, the flue and ventilation, and the boiler’s safety devices.
Your legal duties as a landlord
- Arrange an annual gas safety check on every gas appliance and flue you provide.
- Use a Gas Safe registered engineer — check their ID card and the Gas Safe Register.
- Give tenants the record within 28 days of the check, and to new tenants before they move in.
- Keep each record for at least two years.
- You can renew up to two months early without losing your existing anniversary date.
Since the Renters’ Rights Act 2025 abolished Section 21 on 1 May 2026, an expired certificate no longer blocks a Section 21 notice (there isn’t one) — but gas safety is a strict duty in its own right, and unresolved hazards can undermine a possession case brought on Section 8 grounds. Non-compliance is enforced by the Health and Safety Executive and can bring a fine of up to £20,000 and/or imprisonment, unlimited at the Crown Court.
The annual gas-safety routine
Keeping your Vaillant boiler gas-safe
Book a Gas Safe engineer (service + check together)
Complete the annual check & issue the CP12
Give tenants a copy within 28 days
Keep records 2 years; diary the renewal
Common Vaillant fault codes landlords see
Vaillant boilers (ecoTEC plus, ecoTEC pro and ecoFIT pure ranges) show an “F” fault code when something is wrong. Some point to issues a landlord or tenant can safely resolve; others are strictly engineer territory.
| Code | Usually means | Safe to check yourself? |
|---|---|---|
| F22 | Low water pressure | Yes — top up via the filling loop |
| F28 / F29 | Ignition failure / no gas / flame loss | No — call a Gas Safe engineer |
| F75 | Pump or pressure-sensor fault | No — call a Gas Safe engineer |
Fault codes vary by model, so always check the specific Vaillant manual. Our guide to common combi boiler problems covers the safe checks in more detail. Never repeatedly reset a boiler that keeps locking out on an ignition or gas fault.
For releasing trapped air from radiators cold at the top.
Protects the system against the sludge that causes faults and kettling.
Servicing keeps the certificate straightforward
A gas safety check is a safety inspection, not a service — but booking the two together is sensible. An annual service keeps the boiler efficient, catches wear early, and protects the manufacturer’s warranty, which Vaillant typically conditions on annual servicing. Keeping system pressure in range and dosing the system with inhibitor heads off many of the faults that cause a mid-winter no-heat call-out.
Thinking of replacing the boiler?
Once a boiler is beyond about ten to twelve years old and needing frequent repairs, replacement often makes more sense than another fix. If you replace, ask your engineer whether a low-carbon option suits the property: the government’s Boiler Upgrade Scheme pays a £7,500 grant towards an air source heat pump (or a ground source heat pump) in England and Wales, applied by an MCS-certified installer. The older Renewable Heat Incentive is closed and the proposed Clean Heat Grant never launched — the Boiler Upgrade Scheme replaced them.
FAQ
How often does a Vaillant boiler need a gas safety certificate?
Every 12 months, carried out by a Gas Safe registered engineer, on all gas appliances and flues you provide. Give tenants a copy within 28 days and keep records for at least two years.
Can I do any Vaillant boiler checks myself?
You can safely top up pressure via the filling loop (a common fix for an F22 code), bleed radiators, thaw an external condensate pipe and reset the boiler once. Anything on the gas side must be done by a Gas Safe registered engineer.
What are the penalties for no valid certificate?
Letting without a valid gas safety check is a criminal offence — a fine of up to £20,000 and/or imprisonment, unlimited at the Crown Court, and it can invalidate your insurance.
What does a Vaillant F22 code mean?
Low water pressure. You can usually clear it by topping up via the filling loop to around 1–1.5 bar. If pressure keeps dropping there is a leak that needs investigating.
Written by the Landlords Portal team — experienced UK landlords covering the private rented sector. This article is general information, not legal advice. Always use a Gas Safe registered engineer and check current guidance at HSE.
