Swapping out an old gas hob for a new one should be straightforward. You’ve already got the gas supply, the pipework is in place, and the hob fits the cutout. So why do some installers insist on replacing the gas pipe? And when can you safely reuse what’s already there?
At Gas Hob Installation London, we fit hundreds of hobs across London every year. We see the same questions come up repeatedly. This guide gives you the straight answer — no fluff, no upsell pressure, just what a Gas Safe registered engineer actually checks and what it means for your wallet.
The Short Answer: Usually No, But It Depends
In most cases, you do not need a new gas pipe for a like-for-like hob replacement. The existing pipework can stay. What you do need is a Gas Safe engineer to inspect the pipe, test it for leaks, and confirm it can handle the new hob’s gas load.
However, there are five situations where the pipe must be replaced or modified. Knowing these upfront saves you from nasty surprises on installation day.
When You Can Keep Your Existing Gas Pipe
Your existing gas pipe is fine if all of the following are true:
- Same fuel type: You are not switching from natural gas to LPG, or vice versa
- Adequate pipe diameter: The pipe is 15mm, 22mm, or 28mm and sized correctly for the hob’s kW rating and distance from the meter
- Good physical condition: No corrosion, kinks, or damage to the pipe or joints
- Accessible isolation valve: A working gas isolation valve is present within 1 metre of the hob
- Passing pressure test: The pipe holds pressure during a tightness test and soundness test
A typical domestic gas hob uses 6–10 kW. A 15mm copper pipe can supply this comfortably over short runs (up to 3 metres from the meter). Longer runs or higher-output hobs may need 22mm pipe. Your engineer will check this with a manometer during the installation.
5 Situations Where You Need a New Gas Pipe for Your Hob Replacement
1. The Pipe Is Too Small for the New Hob
Modern hobs are more powerful. A 90cm five-burner model might pull 11–13 kW. A 15mm pipe over a 5-metre run cannot deliver enough gas volume. The flame will be weak, yellow, and inefficient. Your engineer will upgrade to 22mm or 28mm pipe.
2. The Pipe Is Corroded or Damaged
Copper pipe lasts decades, but joints can corrode. Flexible gas hoses (BS EN 14800) have a 10-year lifespan. We replace these as standard during a hob swap. Rigid copper with green verdigris or wall-thinning needs cutting back and re-running.
3. There Is No Isolation Valve
Current Gas Safe regulations require a manual isolation valve within easy reach of the hob. Older installations often lack this. Adding one means cutting the pipe and installing a new valve — effectively modifying the pipework.
4. You Are Switching from Natural Gas to LPG
LPG operates at higher pressure and requires different pipe materials and jointing compounds. The entire supply line from the regulator to the hob must be checked and usually replaced.
5. The Pipe Fails the Tightness Test
Every hob installation requires a gas tightness test. The pipe is pressurised to 1.5 times working pressure and held for a set time. A pressure drop indicates a leak. We cannot legally connect a new hob to a leaking pipe. It must be repaired or replaced.
What a Gas Safe Engineer Actually Checks (Step by Step)
Understanding the process helps you ask the right questions and spot cowboy installer
| Step | What Happens | Why It Matters |
|---|---|---|
| Visual inspection | Engineer examines pipe route, joints, and condition | Identifies corrosion, damage, or non-compliant materials |
| Pipe sizing check | Measures pipe diameter and distance from meter | Confirms gas volume adequacy for hob kW rating |
| Isolation valve test | Checks valve operation and location | Ensures safe emergency shut-off |
| Tightness test | Pressurises pipework and monitors for pressure drop | Mandatory safety check — no pass, no connection |
| Gas rate check | Measures actual gas consumption at full burn | Confirms hob performs to manufacturer spec |
| Flue flow test (if applicable) | Checks extraction if hob is under a canopy | Prevents carbon monoxide buildup |
| Issue certificate | Provides Gas Safety Certificate or Building Regulations Compliance Certificate | Legal proof of safe installation |
Gas Hob Replacement Pipe Costs: What to Budget
| Scenario | Typical Cost (London, 2026) | What’s Included |
|---|---|---|
| Reuse existing pipe | £80 – £120 | Disconnect old hob, tightness test, connect new hob, certificate |
| Add isolation valve | £100 – £160 | As above, plus valve installation and pipe modification |
| Upgrade pipe diameter | £150 – £300 | Pipe replacement from meter branch to hob, fittings, labour |
| Full pipe re-run | £250 – £450 | New pipe through floors/walls, making good, full testing |
| LPG conversion | £200 – £400 | Pipe check, regulator adjustment, burner jet change, test |
Prices vary by property layout, pipe accessibility, and London borough. We always quote upfront after a free site assessment — no hidden fees.
Real-World Examples from Our Jobs
Case 1: Chelsea flat, 2-bed Customer bought a 70cm Neff hob to replace a 15-year-old Bosch. Existing 15mm pipe, 2 metres from meter, perfect condition. We reused it. Total cost: £95. Job took 45 minutes.
Case 2: Hampstead townhouse, 5-bed Customer upgraded to a 90cm Smeg with a wok burner (12.5 kW total). Existing 15mm pipe ran 8 metres from meter. We upgraded to 22mm from the tee. Total cost: £220. The hob now burns blue and powerful.
Case 3: Islington Victorian conversion No isolation valve. Pipe was 1970s steel with rust at the joint. We replaced the final section with copper, added a lever valve, and certified. Total cost: £175. The customer had been quoted £400 elsewhere for a “full system upgrade” they did not need.
Expert Tips: How to Avoid Unnecessary Pipe Replacement Costs
- Check your hob’s total kW output before buying. Divide by 3.6 to get the cubic metres per hour gas rate. A 10 kW hob needs ~2.78 m³/h. A 15mm pipe over 3 metres delivers ~3.5 m³/h. You are safe.
- Photograph your existing pipe and send it to us before booking. We can often tell you over email whether replacement is likely.
- Ask for a breakdown in any quote. “Pipework” is vague. Is it a valve? A diameter upgrade? A full re-run?
- Never accept a hob installation without a tightness test and certificate. It is illegal and dangerous.
- Flexible hoses have expiry dates. If your installer reuses an old hose, question it. We replace them as standard.
Common Mistakes Homeowners Make
- Assuming all replacements are the same: A 60cm four-burner to a 90cm six-burner is not “like for like” in gas demand.
- Buying the hob before checking the pipe: Measure your pipe diameter and distance from the meter first. Or call us for a free pre-purchase check.
- Using a non-Gas Safe fitter: Only Gas Safe registered engineers can legally work on gas pipework in the UK. Check the register at GasSafeRegister.co.uk.
- Ignoring the isolation valve: It is not optional. It is a legal requirement for new installations and replacements where the pipe is modified.
Frequently Asked Questions
Can I use my existing gas pipe for a new hob?
Yes, provided the pipe is the correct diameter, in good condition, has an isolation valve, and passes the mandatory tightness test. A Gas Safe engineer must confirm this before connection.
How do I know if my gas pipe is big enough for a new hob?
Check the hob’s total kW rating and the pipe diameter. A 15mm pipe supplies up to ~3.5 m³/h over short runs. A 10 kW hob needs ~2.78 m³/h. For longer runs or higher kW, 22mm pipe is required. Your engineer will calculate this precisely.
How much does it cost to replace a gas pipe for a hob?
A simple reuse costs £80–£120. Adding an isolation valve runs £100–£160. Upgrading pipe diameter is £150–£300. A full re-run costs £250–£450. We provide fixed quotes after a free assessment.
Do I need a new gas pipe if I am replacing a gas hob with another gas hob?
Not usually. If the new hob has similar gas demand and the existing pipe is sound, it can stay. Only change the pipe if the hob is more powerful, the pipe is damaged, or there is no isolation valve.
What size gas pipe do I need for a gas hob?
Most domestic hobs work on 15mm pipe over short distances (under 3 metres). Higher-output hobs or longer runs need 22mm. Very large commercial-style hobs may need 28mm. Your installer sizes this using gas flow tables.
Does a gas hob replacement need a certificate?
Yes. Any work on gas pipework — including disconnecting and reconnecting a hob — requires a Gas Safety Certificate or Building Regulations Compliance Certificate. This proves the work was done safely and legally.
Can a plumber replace a gas hob pipe?
No. Only a Gas Safe registered engineer can legally work on gas pipework in the UK. A plumber without Gas Safe registration cannot touch the gas supply.
How long does a gas hob replacement take?
A straightforward replacement with pipe reuse takes 45–90 minutes. If pipe modification or replacement is needed, allow 2–4 hours. We always book a half-day slot to avoid rushing.
Conclusion: Get the Right Advice Before You Buy
You probably do not need a new gas pipe for your replacement hob. But “probably” is not good enough when it comes to gas safety. The only way to know for certain is a professional assessment of your existing pipework, your new hob’s requirements, and a proper tightness test.
At Gas Hob Installation London, we offer free, no-obligation site assessments across all London boroughs. We tell you honestly whether your pipe can stay or needs work. No upselling. No jargon. Just safe, certified installations by experienced Gas Safe engineers.
Book your free assessment today — know your costs before you buy your hob.