Tax Deductions Every Plumber Should Be Claiming (But Probably Isn’t)

Here’s an uncomfortable truth. If you’re a self-employed plumber or heating engineer, you’re almost certainly paying more tax than you need to. Not because you’re doing anything wrong — but because you’re not claiming everything you’re entitled to.

It’s not your fault. You’re busy running jobs, chasing payments, and keeping customers happy. Sitting down to figure out which expenses HMRC will and won’t allow is probably the last thing on your list. But that’s exactly how money slips through the cracks.

Think of it this way. Every legitimate business expense you don’t claim is like leaving a £20 note on the floor of every house you visit. You wouldn’t do that. So let’s stop doing it with your tax return.

This guide walks through every tax deduction you should be claiming, what counts, what doesn’t, and some common mistakes that could land you in trouble.

Vehicle and Travel Expenses

Your van is the backbone of your business. You’re in it every day, and it costs a small fortune to keep on the road. The good news is that most of those costs are claimable.

If You Own a Dedicated Work Van

You can claim the actual running costs of your van. That includes:

• Fuel
• Insurance (the business portion)
• Servicing and repairs
• MOT
• Road tax
• Breakdown cover
• Tyres

If you use the van exclusively for work, you claim 100% of these costs. If there’s some personal use mixed in (the school run, weekend trips), you’ll need to work out a fair business-use percentage. Most plumbers and heating engineers find this sits somewhere between 80% and 95%.

If You Use a Personal Vehicle

You can claim 45p per mile for the first 10,000 business miles, then 25p per mile after that. This is called the simplified mileage method, and it covers fuel, wear and tear, insurance — everything. You just need a record of the journeys.

For most plumbers covering 15,000–25,000 business miles a year, the mileage allowance alone could be worth £5,500 to £8,250.

Don’t Forget These Travel Costs

Parking charges at job sites, congestion zone charges, toll fees, and the Dart Charge — all claimable. Even parking fines are not allowable, so don’t try that one. But genuine parking costs? Absolutely.

Tools and Equipment

Every spanner, pipe cutter, and multimeter you buy for work is a claimable expense. That includes:

• Hand tools (pipe wrenches, cutters, spanners, screwdrivers)
• Power tools (drills, SDS hammers, pipe freezing kits)
• Diagnostic equipment (flue gas analysers, pressure gauges, multimeters)
• Replacement parts you carry in the van (fittings, valves, common spares)
• Consumables (solder, flux, PTFE tape, silicone)

If you’re spending £500–£2,000 a year on tools and small equipment (which most heating engineers are), that’s a direct reduction in your taxable profit. A £1,000 tool spend saves a basic-rate taxpayer £200 in tax and a higher-rate taxpayer £400.

Clothing and PPE

This one catches people out. The rule is simple but strict.

You can claim for: work boots with steel toecaps, hi-vis jackets, overalls, boiler suits, hard hats, gloves, safety glasses — anything that’s clearly protective equipment or has your company branding on it.

You cannot claim for: general clothing, even if you only ever wear it for work. A plain pair of jeans or a jumper you wear on site doesn’t count, because HMRC says you could wear it outside of work. It doesn’t matter that you don’t.

The distinction is whether the clothing is specifically protective or branded. Overalls with your logo printed on them? Claimable. A warm fleece from Screwfix with no branding? Not claimable. Keep that in mind next time you’re ordering workwear.

Training and Professional Development

Keeping your qualifications current isn’t optional in the gas and heating trade. It’s the law. And the costs are fully deductible.

• Gas Safe renewal — your annual registration fee
• ACS assessments — the reassessment you do every five years (and any top-ups)
• OFTEC registration — if you work with oil
• Unvented hot water qualifications — G3 courses and renewals
• Manufacturer training — Worcester Bosch, Vaillant, Baxi, Ideal accreditation courses
• Part P electrical courses — if you need them for your work

Between Gas Safe renewal, ACS assessments, and manufacturer courses, a typical heating engineer might spend £1,000–£2,500 a year on training and qualifications. All of it reduces your tax bill.

One important note: the training must be relevant to your existing trade. A refresher course on boiler servicing? Yes. A course to become a qualified electrician when you’ve never done electrical work? HMRC would likely say no — that’s expanding into a new trade, not maintaining an existing one.

Insurance

You’re paying for insurance anyway. Make sure you’re claiming it.

• Public liability insurance — essential for any plumber or heating engineer
• Professional indemnity insurance — covers you for advice and design errors
• Van insurance — the business-use element
• Tool insurance — covers theft from your van (worth having and worth claiming)
• Employer’s liability — if you have staff or use labour

These policies typically add up to £800–£2,000 a year depending on your cover levels. Every penny is an allowable expense.

Phone and Broadband

You use your phone constantly — calling customers, checking job management apps, ordering parts, managing your diary. Those costs are claimable.

If you have a dedicated work phone: the full contract cost is a business expense.

If you use your personal phone for work: you can claim the business proportion. If you estimate that 60% of your usage is work-related, you claim 60% of the bill. Be reasonable with your estimate — HMRC won’t challenge a sensible split, but claiming 95% on your only phone might raise an eyebrow.

The same applies to your home broadband if you use it for admin, quoting, or accessing cloud-based software. A 25–50% claim on your broadband is usually reasonable for most trades businesses.

Home Office Costs

If you do any admin from home — quoting, invoicing, bookkeeping, ordering materials, answering emails — you can claim for the cost of working from home.

You have two options:

The simplified method: Claim a flat rate based on your hours. If you work from home 25–50 hours a month, you can claim £10 per month. At 51–100 hours, it’s £18 per month. Over 101 hours, it’s £26 per month. Most plumbers doing their own admin will fall into the £10–£18 range, giving them £120–£216 a year.

The actual costs method: Work out the proportion of your home used for business and claim that percentage of your household bills (heating, electricity, council tax, mortgage interest or rent). This can sometimes give you a better figure, but it requires more record-keeping.

Either way, it’s free money that most sole traders never bother to claim.

Marketing Costs

Everything you spend on getting your name out there is a business expense:

• Your website (hosting, domain, design)
• Google Ads and Facebook advertising
• Branded uniforms with your company logo
• Van livery and signwriting
• Business cards and printed materials
• Checkatrade, MyBuilder, or Bark subscriptions
• Trustpilot or Google review management tools

Van livery alone might cost £500–£2,000 and it’s fully deductible. Checkatrade membership runs around £600–£1,000+ a year depending on your lead costs. These add up, and they all count.

Software and Subscriptions

If you’re running your business with any kind of technology (and you should be), those subscriptions are allowable expenses:

• Accounting software — Xero, FreeAgent, QuickBooks
• Job management apps — Tradify, ServiceM8, Commusoft, Jobber
• Stock and parts tracking apps
• Cloud storage — Dropbox, Google Drive, iCloud
• Quote and invoice software

With Making Tax Digital requirements tightening, digital record-keeping software isn’t just helpful — it’s becoming essential. Claim the cost.

Professional Memberships

Annual registration and membership fees for trade bodies are fully deductible:

• Gas Safe Register
• CIPHE (Chartered Institute of Plumbing and Heating Engineering)
• WaterSafe
• OFTEC
• Relevant trade unions or associations

These might only be £100–£300 each, but they add up across multiple memberships. They’re easy to forget at tax return time, so keep the confirmation emails.

Pension Contributions — The Big One Most Sole Traders Miss

In my eyes, this is the single most overlooked tax deduction for self-employed plumbers and heating engineers. If you’re employed, your employer automatically enrols you in a pension. When you’re self-employed, nobody does it for you. And because nobody does it for you, most sole traders simply don’t do it at all.

That’s a double loss. You’re missing out on retirement savings and missing out on the tax relief.

Here’s how it works. If you’re a basic-rate taxpayer and you put £100 into a pension, it only costs you £80. The government tops up the other £20 automatically. If you’re a higher-rate taxpayer, you can claim a further £20 back through your Self Assessment, meaning £100 in your pension effectively costs you just £60.

If you contributed £200 a month into a pension, that’s £2,400 a year in contributions with £480–£960 in tax relief depending on your rate. Over 20 or 30 years, that compounds into a serious amount of money.

Don’t leave this one on the table. It’s genuinely one of the best tax advantages available to you.

Capital Allowances — Big Purchases, Big Tax Relief

When you buy something substantial for your business — a new van, a large piece of equipment, significant tool stock — you don’t just deduct the cost as a normal expense. It goes through something called capital allowances.

The good news is that the Annual Investment Allowance (AIA) lets you deduct up to £1,000,000 of qualifying capital expenditure in the year you buy it. For most plumbing and heating businesses, this means you can deduct the full cost of:

• A new or used work van
• Large diagnostic or testing equipment
• Boiler stock (if you buy in bulk)
• Specialist machinery or fabrication tools

Consider this: if you buy a van for £25,000, you can deduct the full amount against your profit in that tax year. For a basic-rate taxpayer, that’s a tax saving of £5,000. For a higher-rate taxpayer, it’s £10,000.

The timing of big purchases matters. If you’re planning to buy a van, it’s worth talking to your accountant about when to do it to get the most benefit. If you’re also thinking about the right business structure, the way capital allowances work might affect that decision too.

Summary: What You Could Be Claiming

Here’s a snapshot of common deductions and what they might be worth in a typical year for a self-employed plumber or heating engineer:

That’s before capital allowances on any big purchases. The tax saving on the figures above could easily be £1,600–£10,500+ depending on your tax rate. That’s real money, sitting right there, waiting to be claimed.

Common Mistakes to Avoid

Claiming expenses isn’t complicated, but there are some pitfalls that trip people up. Let’s explore the ones we see most often.

Claiming Personal Expenses as Business Costs

If it’s not genuinely for work, don’t claim it. A takeaway on the way home from a job isn’t a business meal. Your Netflix subscription isn’t a business expense. HMRC knows the difference, and if they ever look into your return, mixed personal and business claims are the first thing they check.

Not Keeping Receipts

You need to keep records of your expenses for at least five years after the 31 January filing deadline. No receipt, no claim. It’s that simple. Use an app like Dext or Hubdoc to photograph receipts the moment you get them. The ink fades, the paper crumbles, and by January you’ll have lost half of them if they’re sitting in your glovebox.

If you’re working under CIS, good record-keeping is even more important to make sure your deductions are credited properly.

Missing the Deadline

Your Self Assessment tax return for the 2025/26 tax year is due by 31 January 2027 (online). Miss it and you’ll get an automatic £100 penalty, with further penalties stacking up the longer you leave it. More importantly, if you file late, you can’t claim all those deductions until it’s submitted. File on time, claim everything, pay less tax.

Guessing Instead of Recording

Estimating your mileage or rounding up your expenses might seem harmless, but if HMRC opens an enquiry, you need to back up every figure with evidence. A simple mileage log (even a spreadsheet) and photographed receipts are all you need. The five minutes a day it takes will save you hours of stress if HMRC ever comes knocking.

Stop Leaving Money on the Table

Most plumbers and heating engineers we speak to are surprised by how much they can claim. Not because the rules are hidden — but because nobody ever showed them the full picture. You’ve been so focused on doing great work for your customers that the tax side of things gets pushed to the back of the queue.

That changes now. Go through this list, check what you’re already claiming, and start tracking what you’re not. Even picking up two or three deductions you’ve been missing could save you hundreds — or thousands — every year.

Think you might be missing deductions? Book a free tax review and let’s find out what you’re leaving on the table.

If you’re serious about building a better plumbing or heating business, the Together We Count books are your next step. The Quote Handbook helps you price your work with confidence — grab your copy on Amazon. The Systems Handbook gives you the frameworks to run your business properly, available in Kindle, Paperback, and Hardback — or grab the Hardcover edition here.