Sole Trader vs Limited Company for Heating Engineers: Which Is Right for You?

Sole Trader vs Limited Company for Heating Engineers: Which Is Right for You?

It is one of the most common questions we hear from heating engineers and plumbers: “Should I go limited?” And the honest answer is that there is no single right answer. It depends entirely on your circumstances, your income, and where you want to take your business.

Consider this: choosing your business structure is a bit like choosing between a combi boiler and a system boiler. Both do the job, but which one is right depends on the property, the demand, and the long-term plan. Get it wrong and you are either overpaying or missing out.

In this guide, we will walk through exactly what each structure means for your heating business, compare the tax at three different income levels using real 2025/26 figures, and help you work out when switching makes sense.

What Each Structure Actually Means for Your Heating Business

Sole Trader: You Are the Business

As a sole trader, there is no legal separation between you and your business. You keep all the profits, but you are also personally responsible for everything — every debt, every liability, every claim.

The admin is straightforward. You register with HMRC, file a Self Assessment tax return each year, and keep records of your income and expenses. That is essentially it.

For many heating engineers starting out or earning modest profits, this simplicity is a genuine advantage. Less paperwork means more time on the tools.

Limited Company: A Separate Legal Entity

A limited company is its own legal “person.” It earns the money, pays Corporation Tax on profits, and then you extract what you need through a combination of salary and dividends.

You become a director and shareholder of the company. The key difference is limited liability — if something goes wrong, the company’s assets are at risk, not your personal ones (in most circumstances). For heating engineers doing boiler installations and gas work, where a faulty installation could lead to a significant claim, that protection is worth thinking about seriously.

The trade-off is more admin: annual accounts, a Confirmation Statement to Companies House, Corporation Tax returns, payroll for your salary, and stricter rules around how you take money out.

Tax Differences at Different Income Levels (2025/26)

Let’s get into the numbers. We will compare the tax position at three profit levels: £40,000, £60,000, and £80,000. These are profits after allowable business expenses.

For the limited company examples, we are using the most common strategy: paying yourself a salary at the Personal Allowance level (£12,570) and taking the rest as dividends. This is a simplified illustration — your actual position will depend on your specific circumstances.

At £40,000 Profit

Sole Trader:

• Income Tax: £27,430 at 20% = £5,486
• Class 4 National Insurance: £27,430 at 6% = £1,646
• Total tax and NI: £7,132
• Take-home: approximately £32,868

Limited Company (salary £12,570 + dividends):

• Employer’s NI on salary: £7,570 at 15% = £1,136
• Corporation Tax (19% small profits rate): £26,294 at 19% = £4,996
• Dividend Tax (8.75% basic rate): £1,820
• Total tax and NI: £7,952
• Take-home: approximately £32,048

Verdict at £40,000: The sole trader comes out roughly £800 better off. Once you factor in higher accountancy fees for a limited company (typically £1,000–£1,500 more per year), staying sole trader is the clear winner at this level.

At £60,000 Profit

This is where things start to shift. As a sole trader, you are now paying 40% higher-rate tax on everything above £50,270.

Sole Trader:

• Income Tax: £37,700 at 20% + £9,730 at 40% = £11,432
• Class 4 NI: £37,700 at 6% + £9,730 at 2% = £2,457
• Total tax and NI: £13,889
• Take-home: approximately £46,111

Limited Company (salary £12,570 + dividends):

• Employer’s NI on salary: £1,136
• Corporation Tax (19% small profits rate): £46,294 at 19% = £8,796
• Dividend Tax (all within basic rate band at 8.75%): £3,237
• Total tax and NI: £13,169
• Take-home: approximately £46,831

Verdict at £60,000: The limited company saves you around £720 in tax. After accounting for higher accountancy costs, it is roughly break-even — but you also gain limited liability protection, which for a heating engineer carrying out gas and boiler work has real value. This is the tipping point where going limited starts to make sense.

At £80,000 Profit

At this level, the sole trader is paying 40% on a large chunk of income, while the limited company structure offers more planning options.

Sole Trader:

• Income Tax: £37,700 at 20% + £29,730 at 40% = £19,432
• Class 4 NI: £37,700 at 6% + £29,730 at 2% = £2,857
• Total tax and NI: £22,289
• Take-home: approximately £57,711

Limited Company (salary £12,570 + dividends + pension contributions):

At £80,000 profit, company profits sit in the marginal relief band (between £50,000 and £250,000), so the effective Corporation Tax rate is slightly above 19%. This is where smart extraction planning makes a real difference.

A common strategy is to make employer pension contributions through the company. This reduces the company’s taxable profit (keeping it within the £50,000 small profits threshold) and builds your retirement pot in a highly tax-efficient way. For example, with a £17,000 employer pension contribution:

• Employer’s NI on salary: £1,136
• Employer pension contribution (tax-deductible for the company): £17,000
• Corporation Tax (19% on reduced profit of £49,294): £9,366
• Dividend Tax (8.75% basic rate): £3,450
• Total tax and NI: £13,952
• Take-home (cash + pension pot): approximately £66,048

Verdict at £80,000: With pension planning, the limited company puts over £8,300 more per year into your pocket (including pension) compared to the sole trader position. Even without pension contributions, the company structure gives you flexibility in how and when you extract profit — you could leave money in the business, time your dividends across tax years, or invest through the company. For a deeper look at the salary and dividend strategy, see our guide on dividends vs salary for company directors.

Quick Comparison Table

Pros and Cons at a Glance

Sole Trader Pros

• Simplicity — register with HMRC, file one tax return, done
• Privacy — no public records at Companies House
• Lower accountancy costs — simpler accounts mean lower fees
• Full control — no company law obligations, just you and HMRC
• Easy to set up and close down — no formal dissolution process

Sole Trader Cons

• Unlimited personal liability — your house, van, savings are all at risk if something goes wrong
• All profit taxed as income — no flexibility in how you extract earnings
• Harder to win larger contracts — some commercial clients prefer working with limited companies
• Higher tax at higher income levels — 40% Income Tax plus NI above £50,270

Limited Company Pros

• Tax efficiency at higher incomes — significant savings once profits consistently exceed £50k
• Limited liability — particularly relevant for heating engineers doing gas installations where a fault could lead to a serious claim
• Professional image — “Ltd” after your name can open doors to commercial and new-build contracts
• Flexible profit extraction — salary, dividends, pension contributions, retained profits
• Easier to bring on partners — issue shares rather than restructuring the whole business

Limited Company Cons

• More admin and compliance — annual accounts, Corporation Tax returns, payroll, Companies House filings
• Public accounts — your financial information is visible at Companies House (though small company exemptions limit what you must disclose)
• Stricter rules on taking money out — you cannot just transfer company money to your personal account whenever you like
• Higher accountancy fees — expect to pay £1,000–£1,500 more per year compared to sole trader accounts
• Making Tax Digital requirements — limited companies must keep digital records and file quarterly. See our Making Tax Digital guide for more details

When Does It Make Sense to Switch?

In my eyes, the tipping point is when your profits are consistently above £40,000–£50,000 per year. The key word there is consistently. One good year does not necessarily justify the switch — the extra admin and accountancy costs need to be worthwhile over the long term.

Other signals that it might be time to go limited:

• You are regularly turning down commercial or subcontracting work because clients want to deal with a limited company
• You want to bring a family member or business partner into the business
• The liability risk of your work is increasing — more boiler installations, bigger contracts, commercial projects
• You want to start building a pension pot tax-efficiently through employer contributions
• You are planning to grow and eventually employ others

If you are working as a subcontractor under the Construction Industry Scheme (CIS), the structure decision also affects how CIS deductions work and what you can reclaim. It is worth understanding both sides before making the move.

What Does the Transition Involve?

Switching from sole trader to limited company is not as daunting as it sounds, but there are several steps to get right:

1. Register your company at Companies House — choose your company name, appoint directors, and file the incorporation documents. This can be done online and typically costs £12–£50.
2. Register for Corporation Tax with HMRC — you must do this within three months of starting to trade through the company.
3. Open a business bank account — the company needs its own separate bank account. You cannot use your personal account.
4. Set up payroll — to pay yourself a salary, you need to register as an employer with HMRC and run a payroll (even if you are the only employee).
5. Notify your existing clients and suppliers — contracts, invoices, and insurance all need to be transferred to the new company name.
6. Update your Gas Safe registration — your Gas Safe certificate needs to reflect the new business entity.
7. Review your insurance — public liability, professional indemnity, and any other policies need to be in the company’s name.
8. Consider VAT registration — if you are approaching the £90,000 VAT threshold, the switch is a good time to sort this out. See our VAT guide for plumbers and heating engineers for more on this.
9. Close your sole trader affairs — file a final Self Assessment return covering the period up to incorporation.

The whole process typically takes two to four weeks when done properly. A good accountant will handle most of this for you.

IR35 and Subcontracting: An Important Consideration

Many heating engineers do not just work for their own customers. Subcontracting for larger firms, housing associations, or facilities management companies is common in this trade. If you operate through a limited company and provide your services to a client who controls how, when, and where you work, IR35 may apply.

IR35 is the legislation designed to identify workers who would be employees if they were not operating through their own company. If HMRC determines your contract falls inside IR35, you will be taxed as if you were an employee — wiping out most of the tax advantages of a limited company.

Since April 2021, for medium and large businesses, the responsibility for determining your IR35 status sits with the end client, not you. For small businesses, you still make the determination yourself.

Key factors that affect your IR35 status:

• Control — does the client dictate how you do the work, or do they just set the outcome?
• Substitution — could you send another qualified engineer to do the job in your place?
• Mutuality of obligation — is the client obliged to offer you work, and are you obliged to accept it?

If you are doing varied work for multiple clients, providing your own tools, and have genuine control over how you deliver the service, you are more likely to be outside IR35. If you are essentially working full-time for one company on their schedule, using their systems, that is a red flag.

This does not mean you should avoid going limited if you subcontract. It means you need to structure your contracts and working practices carefully. We help heating engineers get this right so they are not caught out.

Corporation Tax Rates: A Quick Note

Since April 2023, Corporation Tax in the UK works on a tiered system:

• 19% small profits rate — for company profits up to £50,000
• 25% main rate — for company profits over £250,000
• Marginal relief — for profits between £50,000 and £250,000 (the effective rate gradually increases from 19% to 25%)

Most heating engineers operating as a one-person limited company will fall comfortably within the small profits rate of 19%. If your company profits are regularly above £50,000, speak to your accountant about strategies to manage the marginal relief band — such as employer pension contributions or timing of expenses.

So, Which Is Right for You?

Let’s explore a simple way to think about it:

• Profits under £40,000 — stay sole trader. The simplicity and lower costs outweigh any tax saving.
• Profits between £40,000 and £50,000 — this is the grey area. If liability protection and professional image matter to you, going limited could be worthwhile even before the tax numbers stack up.
• Profits consistently above £50,000 — a limited company is almost certainly worth considering. The tax savings, pension flexibility, and liability protection become significant.

But remember, these numbers are just one part of the picture. Your personal circumstances, plans for the business, attitude to admin, and risk profile all matter. There is no one-size-fits-all answer — just the right answer for you.

Not Sure Which Structure Is Right for Your Business?

Book a free consultation and we will run the numbers for you. We work with heating engineers and plumbers across Sheffield and beyond, and we will give you a clear, honest comparison based on your actual figures — not generic advice. No obligation, no jargon, just straight answers.