How do I claim a CIS refund as a gas engineer?

On your tax return, once the tax year ends on 5 April. For 2026-27 a sole trader gas engineer can file from 6 April 2027. Under Making Tax Digital, the refund is requested separately through HMRC online services.

Under the Construction Industry Scheme (CIS), a contractor takes 20% from the labour part of what it pays you if you are registered, or 30% if it cannot verify you. That is an advance payment towards your Income Tax and National Insurance. Gas work paid for by householders has no deduction, so the CIS side is often one or two install contracts in a year of domestic jobs. Over-deducted CIS is claimed back through your tax return. The sooner after 5 April you file, the sooner HMRC can repay you. This page is for sole traders and follows GOV.UK as checked on 18 October 2026. A limited company uses its deductions through its payroll instead, as our guide on whether a limited company can claim back CIS deductions explains.

Which route applies to you

Making Tax Digital for Income Tax (MTD) started on 6 April 2026 for sole traders whose 2024-25 return showed self-employed and rental income over £50,000 before costs. It starts on 6 April 2027 if the 2025-26 return shows over £30,000. For CIS work, in our reading the gross pay before deductions is what counts, because that is the turnover on your return.

Which gas and heating jobs have a deduction

A repair contract that includes making good to the building is caught. Our guide on whether CIS applies to plumbers and heating engineers covers the edge cases.

A worked example for a gas engineer

Ravi is a self-employed gas engineer outside Scotland with no other income. In 2026-27 householders pay him £22,000 for boiler swaps, servicing and repairs, including £7,000 of boilers and parts he bought. One developer pays him £25,000 to install heating and gas supplies in six new houses: £18,000 labour and £7,000 for boilers, radiators and pipe he bought. The developer takes 20% of the labour only, which is £3,600. His van, tools, flue gas analyser, insurance and phone cost £6,000.

Ravi gets no refund. The deduction is still his money: it pays most of his bill, and he pays the £151.80 balance by 31 January 2028. Had the developer taken 20% off the whole £25,000, it would have deducted £5,000 and he would be due £1,248.20 back, after waiting for the year to end. These are 2026-27 rates. Class 2 National Insurance is treated as paid because his profit is above £7,105. This is an example only.

Steps to claim your CIS refund

1. Collect every payment and deduction statement for the tax year, 6 April to 5 April. A contractor who takes a deduction must give you one within 14 days of the end of that tax month, so the last one for 2026-27 is due by 19 April 2027.
2. Ask for copies of any missing statements. If a contractor has closed, write to HMRC with your details, the contractor's details, the dates you were paid and why you have no statements.
3. Check each statement against your bank account, and that the deduction came off the labour, not the boilers and pipe on your invoice.
4. Total your householder income, including card and cash payments, and keep your merchant receipts for every boiler and part.
5. If you are not in MTD for the year, put your total turnover and your CIS deductions on your Self Assessment return, give your bank details and file online.
6. If you are in MTD, check the CIS deductions HMRC has added to your MTD tax return, correct them in your software if needed, submit, then request any refund through your HMRC online services account.

What this means for you

Ravi's 2024-25 return was under £50,000 and his 2025-26 return showed over £30,000, so he joins MTD on 6 April 2027. His 2026-27 return is still an ordinary Self Assessment return. From 2027-28, HMRC adds his deductions to his MTD tax return and he requests any refund separately.

The deadline for a 2026-27 return is 31 January 2028. If you are due money back, filing in April 2027 instead puts your claim in up to ten months sooner. If your work is mostly for householders, expect the deductions to cover only part of your bill, and set money aside from domestic jobs as you go.

Be wary of anyone who promises a refund by a set date. Only HMRC decides when it pays.

If something looks wrong

• A contractor took 30%. GOV.UK says your details must match your registration exactly. Speak to the contractor; the extra still counts on your return.
• A contractor deducted from a boiler swap or a service. On their own these are outside CIS, so raise it with the contractor. If it is not put right, in our reading the deduction on your statement still goes on your return.
• HMRC's figures differ from your statements. Our guide on checking your CIS deductions with HMRC sets out each route.

Use the free MTD check to see when MTD starts for you, and the trades section for more guides for gas engineers.