Best Invoicing App for Gas Engineers UK 2026: Gas Safe Numbers, CP12 Certificates and CIS Deductions

Gas engineer invoicing carries more compliance weight than most trades. Your Gas Safe registration number needs to appear on gas work invoices. CP12 landlord certificates need to be referenced and often attached. CIS subcontractors must show the labour and materials split so the main contractor can apply the correct deduction. Getting any of this wrong delays payment or creates compliance issues with HMRC.

This guide compares the best invoicing apps available to UK gas engineers in 2026, focusing on Gas Safe field support, CP12 attachment workflows, CIS invoice formatting, VAT handling, and overall cost. Whether you are a sole trader running service calls or an engineer managing a team of engineers across multiple landlord properties, there is an option here to suit you.

Gas Engineer Invoice Checklist

Every invoice you issue for gas work should include the following:

• Gas Safe registration number (mandatory on any invoice for gas work)
• Business name and address
• Invoice number
• Work description including appliance make, model and location
• Labour and materials itemised separately (critical for CIS subcontractors)
• Gas Safety Certificate reference or CP12 number where applicable
• VAT at 20% if you are VAT registered, plus your VAT number
• Payment terms stating when payment is due

App Comparison

App Reviews

Sleepless Tradesman

Sleepless Tradesman is free to use with no subscription required, making it a practical starting point for sole trader gas engineers who want professional invoicing without a monthly overhead. The app supports CIS invoice formatting with labour and materials shown as separate line items, which means your main contractor can apply the correct deduction rate without needing to ask you to reissue the invoice.

You can add a card payment link directly to the invoice so homeowners can pay on the day. The homeowner marketplace also gives you access to new boiler and central heating leads without paying per-lead fees. The main limitation for gas engineers is that there is no dedicated Gas Safe registration number field built in — you add it as a custom footer line or note on the invoice template. For most engineers this takes one minute to set up and is not a meaningful barrier.

Commusoft

Commusoft is built specifically for heating and plumbing businesses and includes a dedicated Gas Safe registration number field on invoices as standard. Its standout feature for gas engineers is the CP12 workflow — Gas Safety certificates are generated within the same job record and linked directly to the invoice, so landlords receive both documents in one email without any manual attachment step.

Commusoft also stores full appliance history per property, which is valuable if you manage large landlord portfolios where the same boiler appears on multiple annual certificates. The main downside is cost. At £45 to £150 per month depending on the plan and team size, it is one of the more expensive options on this list, and it has no native CIS support, so engineers doing subcontract work still need to manage the labour and materials split manually.

Powered Now

Powered Now is a UK-built job management app designed with tradespeople in mind, and gas engineers are among the core use cases. It includes a Gas Safe number field on invoice templates, gas safety certificate templates you can complete on your phone or tablet in the field, and basic CIS handling for subcontractors who need to show the labour and materials split.

The pricing is more accessible than Commusoft, starting at around £19 per month for sole traders. The product is smaller and has fewer integrations than some competitors, but for a gas engineer who wants a straightforward UK-focused tool that handles certificates and invoices in one place, Powered Now covers the core requirements at a reasonable price.

Tradify

Tradify produces clean, professional invoices and has a solid Xero integration that makes MTD VAT filing straightforward for VAT-registered gas engineers. It is a well-designed app with good mobile support and a workflow that suits engineers who move between jobs quickly and want to invoice from the van.

The main gaps for gas engineers are the absence of a native Gas Safe registration number field and no built-in CIS support. You can add the Gas Safe number manually in a notes field or invoice footer, but it requires remembering to do it on every invoice rather than it pulling from your profile automatically. Engineers doing subcontract work will need to manage the CIS labour and materials split manually within the line item structure.

ServiceM8

ServiceM8 charges per job rather than a flat monthly fee at lower volumes, which suits gas engineers with variable workloads. You can build custom fields into job cards and invoice templates, so adding a Gas Safe number field is possible through configuration. CP12 documents can be attached to the email sent alongside the invoice.

Like Tradify, ServiceM8 has no native Gas Safe field and no CIS support, so both require manual setup or workarounds. At higher volumes the per-job pricing model can become more expensive than a flat subscription. For engineers doing a mix of homeowner service calls and some subcontract work, it covers the basics but requires more setup effort than a gas-specific tool.

CIS for Gas Engineers: What You Need to Know

• If you work as a subcontractor for a main contractor registered for CIS, your invoices must show labour and materials as separate line items. The main contractor deducts 20% (or 30% if you are not CIS registered) from the labour element only and pays it to HMRC on your behalf.
• The deduction is not a final tax payment. You claim it back through your self-assessment tax return at the end of the tax year as a credit against your tax liability. Keep all CIS deduction statements from your contractors as you will need them to complete your return accurately.
• Always confirm whether your main contractor is registered for CIS before starting subcontract work. If they are registered and you do not provide a correctly formatted invoice, they may withhold the full 30% unregistered rate rather than the 20% standard rate, which affects your cash flow even though it is recoverable.

Verdict

For gas engineers who want no monthly cost and a CIS-ready invoice format, Sleepless Tradesman is the strongest starting point. Add your Gas Safe number as a footer line and you have a compliant invoice at no cost with card payment built in.

If you manage a landlord portfolio and need CP12 certificates generated and attached within the same workflow, Commusoft justifies its cost. The integrated certificate-to-invoice workflow saves meaningful time across a large number of annual gas safety checks.

For a UK-focused mid-range option with Gas Safe field support and certificate templates, Powered Now sits in a practical middle ground. Tradify and ServiceM8 are solid general trade apps but require more manual effort from gas engineers to cover the compliance requirements specific to the trade.

Frequently Asked Questions

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