Does CIS apply to gas engineers?

CIS sits in a strange spot for gas engineers: the same van, the same tools and the same boiler can be inside or outside the scheme depending on who is paying and what the contract covers. Get it wrong one way and a contractor deducts 30% you didn't plan for; get it wrong the other way and you are running deductions you never needed. Here is where the line actually sits.

What is the Construction Industry Scheme?

CIS is HMRC's scheme for payments from contractors to subcontractors for construction work. When a contractor pays you for work within the scheme, they deduct a slice of the payment and pass it to HMRC, and those deductions count as advance payments towards your tax and National Insurance, reconciled when you do your Self Assessment. It is not an extra tax, but it is a real cashflow and admin layer. And it only exists between businesses: a private householder is not a contractor, so work invoiced to a homeowner is never within CIS.

Is gas work inside or outside CIS?

The line comes straight from HMRC's own manual, and it is sharper than most people expect. Installing a system of heating in a building is a construction operation within the scheme. Repairs are not: the manual states that repairs to building service systems are outside the scope of CIS, and then deals with the boiler question directly. Even where the repaired or replaced item is a significant component of the overall system, “such as a central heating boiler, its replacement does not constitute 'the installation of a system of heating'” and so does not fall within CIS. In plain terms: first-fix heating on a new build, or a full system install subcontracted from a builder, is CIS work. A boiler swap in an existing system is not, because you are repairing a system that already exists, not installing one.

One rule can pull otherwise-outside work back in: mixed contracts. CIS340 puts it bluntly: “If a contract includes some work that is within the scheme and some that is nothing to do with construction at all then all payments made under that contract will come within the scheme”, even when the work is invoiced separately. So a boiler replacement priced as its own standalone job for a builder can sit outside the scheme, while the same replacement wrapped inside a wider refurbishment contract is inside it. The contract decides, not the job.

What are the CIS deduction rates?

• Registered subcontractor: the contractor deducts 20% from your payments and passes it to HMRC.
• Not registered: the deduction is 30% instead, which is the expensive way to discover the scheme exists.
• Gross payment status: no deductions at all; you are paid in full and settle your tax through your return.
• Whatever the rate, deductions count as advance payments towards your tax and National Insurance, so they come off your eventual bill or back as a refund.

The deduction is not applied to your whole invoice. Before calculating it, the contractor strips out VAT, the cost of materials you paid for, plant hire, fuel used on the job (other than for travelling) and consumables; the rate applies to what is left, which is essentially your labour. That is why a clean materials and labour split on every invoice is more than good practice here: it is the number the deduction runs on. Manifold's quotes and invoices carry that split as standard, so the contractor's bookkeeper and your accountant are working from the same figures.

How does gross payment status work?

If you would rather be paid in full, you can apply for gross payment status. HMRC's tests: you have paid your tax and National Insurance on time in the past, your business does construction work (or provides labour for it) in the UK, and it runs through a bank account. Then there is a turnover test: for a sole trader, at least £30,000 of construction turnover in the last 12 months, ignoring VAT and the cost of materials, with higher combined thresholds for partnerships and companies. Applying also registers you for CIS if you were not already registered. Gross status is worth having on serious subcontract volume, but it lives or dies on a clean compliance record.

How do you register, and when should you?

Register with HMRC as a CIS subcontractor before the first payment from a contractor lands, because until you do, every payment carries the 30% rate rather than 20%. The trigger is simple: the first time a builder, heating firm or plumbing contractor offers you subcontract work on installs, sort the registration first. And note the scheme cuts both ways. If your own workload grows to the point where you pay other subcontractors for construction work, you take on contractor duties yourself: verifying subcontractors with HMRC, making deductions and filing monthly returns.

When does a gas engineer never touch CIS?

When the whole round is domestic. An engineer whose invoices go to homeowners, private landlords and letting agents, for CP12s, services, repairs and boiler swaps, has no contractor above them and nothing within the scheme, and that describes a large share of the trade. CIS starts the day you take subcontract work from a construction business on installation jobs, and only for that work; your domestic customers carry on exactly as before.

How does CIS interact with VAT?

Through the domestic reverse charge. For building and construction services within CIS supplied between two VAT-registered businesses, the customer accounts for the VAT instead of paying it to you, so your invoice notes the reverse charge rather than adding VAT. Homeowner work is unaffected and carries VAT the normal way if you are registered. If your turnover is anywhere near the registration threshold, the two schemes are worth reading together; our VAT guide covers the threshold and the traps.