Missing gas and water bonding on an EICR: what does it mean?

What is main protective bonding?

It is a cable, usually green and yellow, that runs from the main earthing terminal near your consumer unit to a clamp on each metal service pipe where it comes into the building. Gas, water and oil are the usual ones.

Those pipes are connected to the ground outside, so they are not at the same potential as the earth your electrical installation uses. Bonding ties them together. If a fault puts a voltage on the metalwork of an appliance, bonding stops a dangerous difference building up between that appliance and a pipe you could be touching at the same time. Without it, the protective devices in your board are doing their job with one hand tied.

Bonding is not the same as earthing. Earthing is how the installation connects to the ground in the first place, usually through the supply company’s cable or an earth rod. Using a metal water or gas pipe as the means of earthing is itself a C2, and a different problem from missing bonding.

How does an EICR code a bonding problem?

Inspectors follow Electrical Safety First’s Best Practice Guide 4, which was updated in August 2026 for the current edition of the wiring regulations. For main bonding it sets these out:

• C2, potentially dangerous: no effective main bonding to the metal services entering the building.
• C2: a bonding cable smaller than 6 mm², or one showing signs of heat damage.
• C3, improvement recommended: bonding you cannot get at to inspect or test, or a clamp put on a branch pipe where the connection back to the main pipe is not assured.
• No code: bonding at least 6 mm² with no damage, even if a new installation today would use a thicker cable.

The same guide says that if any item is coded C1 or C2, the overall condition must be reported as unsatisfactory. If there are only C3s, it can be reported as satisfactory. So missing bonding on its own is enough to fail the report, and a slightly thin cable on its own is not.

What does not need bonding?

More than most people think, and this is where reports sometimes go wrong.

If your water and gas come into the building in plastic pipe, there is no incoming metal to bond. NICEIC’s published answer is plain about it: where the incoming pipework is plastic, main bonding is not required. A short length of copper inside the house may still need looking at, but that is a different test and a different answer.

Best Practice Guide 4 lists two myths outright. Missing bonding to boiler pipework is not a defect where that pipework is not itself bringing in an outside earth potential, and neither is missing bonding to metal sinks and baths. Bathroom supplementary bonding is a separate question again, and many modern bathrooms can leave it out. Our bathroom zones article explains when.

Why does bonding come up now, when the house has been fine for years?

Usually for one of three reasons.

• An EICR for a sale, a mortgage or a let. Bonding is one of the first things checked at the board, so it is one of the commonest C2s on older houses.
• You have asked for other work. BS 7671 does not allow an addition or alteration to an installation until the electrician has confirmed the earthing and bonding it depends on are adequate. A new circuit, an EV charger or a new consumer unit can all bring it to light.
• Somebody changed the pipes. A new gas meter, a water main replaced in plastic, or a kitchen refit that moved the pipework can leave a clamp on nothing, or on the wrong pipe.

If you let the property, it is not optional. Under the 2020 regulations for privately rented homes in England, remedial work from a C2 has to be done within 28 days of the inspection, or sooner if the report says so, and you need written confirmation from the electrician to send to the tenant and the council. Our landlord article covers the rest of that duty.

What does fixing it involve?

We find where each metal service enters the building and where the main earthing terminal is, then run a bonding cable of the right size between them. The clamp goes on the pipe on your side of the gas meter or the water stopcock, before the pipe branches off, somewhere it can be seen and reached later, and it carries a permanent safety label.

We do not touch the gas meter or work on the gas pipe. A clamp goes round the outside of the pipe, and anything that would mean disturbing the gas installation is a Gas Safe registered engineer’s job.

Then we test the continuity of each bonding connection back to the main earthing terminal and issue a minor works certificate, which is what clears the C2 and what a landlord sends on.

Here is the part a sales-led quote will not volunteer. Missing bonding is not, on its own, a reason to replace your consumer unit or rewire the house. If those are being recommended, ask which observation on the report each one fixes. And if your bonding is there, at least 6 mm² and undamaged, a C2 for size alone goes further than Electrical Safety First’s own guidance. Ask the inspector to explain it before you pay to put it right.

What changes the price of a bonding upgrade?

It is usually a small job. What makes one bigger than another is the route, not the clamp.

• How far the gas and water entry points are from the consumer unit and the main earth.
• Whether the cable can run through a cupboard, a void or a garage, or has to cross finished rooms.
• Meters in an outside box, which need a neat route through the wall.
• Whether the main earthing terminal and the supply earth are sound, which we check first.
• Any other C2s on the same report, which are often cheaper to put right in the same visit.

Send us the report through our quote page and we will tell you which observations matter and which do not. If you need the inspection itself, see EICRs and electrical safety certificates.

Questions we get asked about this