Righto Tax for Trades · Plumbers and gas engineers
Tax, CIS and Making Tax Digital for self-employed plumbers and gas engineers
Much plumbing and heating work is paid in full, because homeowners and most landlords don’t deduct CIS. For builders, a new heating system or a bathroom fit is inside CIS, while a boiler swap, a service or an extra radiator usually is not. Making Tax Digital counts all of it, before any deduction.
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Righto Tax for plumbers and gas engineers
- Your bank feed becomes your Making Tax Digital quarterly updates.
- Your CIS deductions are matched to your statements and counted in your tax return.
- You confirm every figure before it’s sent, and we never ask for your HMRC password.
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When Making Tax Digital starts for plumbers and gas engineers
It depends on your qualifying income, not your trade. Qualifying income is the total of self-employment and property income before expenses (turnover), not profit.
| Qualifying income | On your tax return for | Making Tax Digital |
|---|---|---|
| Over £50,000 | 2024-25 | Applies since 6 April 2026 |
| Over £30,000 | 2025-26 | Starts 6 April 2027 |
| Over £20,000 | 2026-27 | Starts 6 April 2028 |
Once you’re in, you send HMRC a quarterly update by 7 August, 7 November, 7 February and 7 May, then a tax return after the year ends. MTD for Income Tax does not change how tax is paid or the payment due dates.
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CIS for plumbers and gas engineers
CIS covers installing a whole heating, water, drainage, sanitation or gas supply system in a building, and replacing a whole system counts as installing one. Fitting kitchens and bathrooms is covered too. Repairing, servicing or extending a system is not, and HMRC treats even a new boiler as a replacement part, not a new system. A contract that also includes building work, such as making good a wall after a leak, brings every payment under it into CIS. On a supply-and-fit job, the deduction is worked out after the materials you bought are taken off.
Usually inside CIS
- A new central heating or hot water system
- Replacing a whole heating system
- Fitting a kitchen or bathroom for a builder
- Installing a gas supply in a building
- Water softeners, meters and treatment systems
- A leak repair that includes making good the wall or ceiling
Usually outside CIS
- A boiler swap on its own
- Boiler servicing and maintenance
- Adding a radiator to an existing system
- Fixing a leaking pipe, tap or radiator
- Delivering boilers, pipe or materials only
When CIS applies, a contractor deducts 20% if you’re registered for CIS, 30% if you’re not, and nothing if you have gross payment status. To work out a CIS deduction, the contractor starts with the gross invoice and takes away what the subcontractor paid for VAT, consumable stores, fuel (except for travelling), plant hire, manufacturing or prefabricating materials, and materials; the CIS rate is then deducted from the amount left.
Before you join Making Tax Digital, over-deducted CIS is claimed back through your Self Assessment tax return. Once you are in Making Tax Digital, HMRC adds your CIS deductions to your tax return, and any refund is requested separately through HMRC online services. Either way, the sooner after 5 April the return is filed, the sooner HMRC can repay you.
Free, and it runs in your browser: add your van or mileage, tools and phone, for 2025-26 and 2026-27.
Costs plumbers and gas engineers usually claim
The test for every cost is whether it was for your business. If something is partly personal, only the business part counts.
| Cost | How it’s treated |
|---|---|
| Boilers, cylinders, radiators, pipe and fittings for jobs | Materials for the work you sell. What the customer pays you for them is income, so note which job each merchant order went on. |
| Flue gas analyser, manometer, gas detector and pressure testers | Equipment you keep and use in the business. Calibration and repairs are claimed as maintenance. |
| Press-fit tool, pipe benders, blowtorch and drain camera | Tools you keep for the business. On the cash basis they come off your profit in the year you pay. |
| Gas Safe registration and competent person scheme fees | The law requires registration before you do gas work, so the fee is a cost of the trade. A scheme for self-certifying water or heating work counts too. |
| ACS reassessments and heat pump courses | Allowed when they update skills you already use. HMRC’s own example is a boiler fitter training on heat pumps. First training to enter the trade is not. |
| Certificate and job software | A subscription you renew to issue gas safety records or run jobs is a running cost. |
| Safety boots, knee pads and overalls used only for work | Protective clothing counts. Everyday work trousers and hoodies do not. |
| Parts used on your own home | Not allowable. Goods bought for private use stay out of your expenses, even if bought on a trade account. |
Your van, tools and kit
Most plumbers and gas engineers drive from home to a different call-out or job each day, which HMRC usually treats as travel to temporary workplaces. The van carries both your tools and stock, so it is business equipment, but personal use needs splitting out. Analyser calibration is a running cost of the kit, so keep each calibration invoice with the purchase receipt. If you also run a unit or store, the drive from home to there is commuting, and trips from there to jobs are business.
From 2024-25 the cash basis is the default for sole traders and partnerships without corporate partners, with no turnover limit; traditional (accruals) accounting is an opt-out. Under the cash basis, the cost of equipment bought to keep and use in the business, such as machinery, computers and vans, is claimed as a normal allowable expense rather than a capital allowance. Cars are different: they go through capital allowances.
Simplified expenses for cars and goods vehicles (vans) from 6 April 2026: 55p a mile for the first 10,000 business miles, then 25p; motorcycles 24p. Once used for a vehicle you must keep using it for that vehicle, and it cannot be used for a vehicle already claimed through capital allowances.
Answers for plumbers and gas engineers
- Does CIS apply to plumbers and heating engineers?CIS covers installing whole heating and water systems and fitting kitchens and bathrooms. A boiler swap, extra radiator, repair or service alone is outside.
- What expenses can a self-employed plumber claim?Plumbers can claim pipe and fittings, tools, analysers and calibration, Gas Safe fees, heat pump and bookkeeping courses, van costs and protective gear.
- What expenses can a self-employed gas engineer claim?Gas engineers can claim Gas Safe registration, ACS and other training, analyser calibration, parts, tools and van costs. The gas-specific rules for 2026-27.
- Does CIS apply to work for homeowners?No. Homeowners paying for work on their own home are not CIS contractors, so nothing is deducted. When a private client does bring in CIS, and paying the tax.
- Does CIS apply to materials?CIS is not deducted from materials you buy yourself, VAT, hired plant or consumables. How the contractor works out the deduction, with a worked example.
- Does Making Tax Digital apply to CIS subcontractors?Yes, if you are a sole trader. CIS pay counts before deductions and costs, so £25,600 in the bank can mean MTD from 6 April 2027. How CIS works inside MTD.
- Is my turnover before or after CIS deductions?Before. Your turnover is your full pay before CIS deductions, tested for Making Tax Digital and VAT. The gross payment status test also takes off materials.
- Can I claim my van as a business expense?Yes. Sole traders claim a van with the flat mileage rate, 55p a mile in 2026-27, or with actual costs plus the van's price. How each works and the switch rules.
Questions people ask
A builder took CIS off a boiler swap. Was that right?
Not if the swap was the whole contract. HMRC’s manual treats a new boiler as replacing a part, not installing a system, so it is outside CIS. If the same contract also covered building work, such as making good, every payment under it is covered.
Does a landlord deduct CIS when I service their boilers?
No. CIS 340 excludes servicing and maintaining heating systems, and most landlords are not CIS contractors in the first place. Invoice them in full and put money aside for the tax.
Is a bathroom refit for a builder a CIS job?
Yes. HMRC lists kitchen and bathroom fitting as construction work, so a builder paying you for it deducts CIS. Show the suite and pipe you bought on the invoice, so the deduction is only worked out on your labour.
Can I claim my first gas course if I am changing careers?
Usually not. HMRC’s manual says training to start a new business, or move into an unrelated one, is unlikely to be allowable. Courses that update the gas work you already do, such as ACS reassessments, usually are.
Other trades
Weighing up Hnry, FreeAgent, Starling, Countingup or an accountant? See the options for plumbers and gas engineers side by side.
This is general information to help you understand the rules. It isn't tailored to your circumstances, so check your own position before acting on it.
Sources
- CISR14090: construction operations: building service systems (HMRC manual)
- CISR14240: preparatory, integral and finishing operations (HMRC manual)
- Construction Industry Scheme: a guide for contractors and subcontractors (CIS 340)
- The Gas Safety (Installation and Use) Regulations 1998, regulation 3 (legislation.gov.uk)
- Check if the cost of training could be an allowable business expense (GOV.UK)
- BIM35660: proprietor’s training courses (HMRC Business Income Manual)
- Expenses if you’re self-employed (GOV.UK)
- BIM37620: travel costs to and between sites (HMRC Business Income Manual)
- Use Making Tax Digital for Income Tax: submit your tax return (GOV.UK)
- Find out if and when you need to use Making Tax Digital for Income Tax — checked 15 October 2026
- Work out your qualifying income for Making Tax Digital for Income Tax — checked 17 October 2026
- Use Making Tax Digital for Income Tax: Send quarterly updates — checked 15 October 2026
- How Making Tax Digital works (HMRC campaign site) — checked 17 October 2026
- What you must do as a Construction Industry Scheme (CIS) subcontractor — checked 15 October 2026
- What you must do as a CIS subcontractor: Pay tax and claim back deductions — checked 15 October 2026
- What you must do as a CIS contractor: Make deductions and pay subcontractors — checked 16 October 2026
- Expanding the cash basis — checked 15 October 2026
- Simpler income tax: cash basis — checked 17 October 2026
- Simplified expenses if you're self-employed: Vehicles — checked 16 October 2026