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Contractors who design
Gas and heating engineers need professional indemnity insurance once they design: sizing boilers, calculating heat loss, designing heat pump systems, choosing emitters or giving running-cost estimates. If you only service and repair appliances, your main exposure is accidents, which public liability covers. A home that never gets warm, or bills well above the estimate, is a design or advice failure, and public liability usually won’t pay for it.
Part of: Professional indemnity for design and build contractors
In short
Gas Safe registration is a legal requirement for gas work, but it isn’t insurance and doesn’t protect you against design claims. Professional risk arises when you size and design: Approved Document L expects a heat loss calculation and a sizing method, with new or fully replaced wet systems designed for a maximum 55°C flow temperature where feasible. For heat pumps, MCS MIS 3005-D sets the heat load method, requires a heat-pump-only system to meet 100% of the calculated load, and controls how running-cost estimates are presented. Claims usually allege undersizing, misleading estimates or wrong planning advice.
Last reviewed 5 October 2026 by the Apex professional indemnity team.
A heating engineer who only services and repairs boilers mainly faces accident claims: a gas escape, a scald, a leak that ruins a kitchen ceiling. Public liability (PL) is built for those. The picture changes when you decide what a system should be: you size a boiler, calculate heat loss, choose radiators, design a heat pump system or tell a customer what it will cost to run. Those are professional judgements, and a mistake in them usually causes financial loss rather than accidental damage.
PL policies generally exclude claims that a system failed to perform as intended, and they don’t pay for pure financial loss. A house that never gets warm, bills far above the estimate, or a heat pump the council orders to be moved are design and advice failures. Professional indemnity (PI) insurance is the policy written for them.
The move to heat pumps has pushed more heating businesses into design. Heat pumps are far less forgiving of rough sizing than gas boilers, the design standard is detailed and written down, and customers are often spending grant-supported money on the strength of your figures.
These scenarios are illustrative, not real claims. They show where heating engineers’ professional judgement is most often challenged.
None of these needs an accident. Each is an allegation that you didn’t calculate, design, advise or administer with the care expected of a competent heating professional.
Experts judging a heating claim compare your work with the following. The Building Regulations guidance and planning rules are for England; Gas Safe Register covers the UK, the Isle of Man and Guernsey.
| Rule or standard | What it says | Why it matters to you |
|---|---|---|
| Gas Safety (Installation and Use) Regulations 1998, reg. 3 | Nobody may work on a gas fitting unless competent, and employers and self-employed people doing gas work must belong to a class of persons approved by HSE. Gas Safe Register is that official register, and by law all gas businesses must be on it. | Registration is a legal condition of gas work. It is not insurance and doesn’t cover design or advice claims. |
| Approved Document L, volume 1, paras 5.8 to 5.10 | Heating should be specified from a heat loss calculation and a sizing method, and should not be significantly oversized. A new or fully replaced wet system should be sized to work at a maximum flow temperature of 55°C where feasible. | Your sizing and emitter choices are measured against this guidance. |
| MCS MIS 3005-D, issue 3.0 | The heat pump design standard, mandatory since 5 December 2025 for designers certified to it. Contractors certified to MCS:2025 must follow MIS 3005-D:2025. It sets the heat load method, the sizing rule and what the customer must be told before signing. | If you design to MCS, the standard is the yardstick for any sizing or estimate claim. |
| Permitted development for air source heat pumps (GPDO 2015, Class G) | A unit installed without planning permission must comply with the MCS Planning Standards. Since 29 May 2025 a detached house can have up to two units and a house unit can be up to 1.5 cubic metres. Units still can’t go on a pitched roof or anywhere at a listed house and, outside conservation areas, can’t go on a wall facing a highway above the ground floor. | Customers rely on you to say whether planning permission is needed. |
| Boiler Upgrade Scheme | Grants in England and Wales go through MCS certified installers, who apply on the property owner’s behalf. | Administrative mistakes can cost the customer the grant, and they will look to you. |
| Defective Premises Act 1972, s.2A | For work on existing homes completed after 28 June 2022, a business must do the work in a workmanlike or professional manner, with proper materials, so that the dwelling is fit for habitation as regards that work. Later owners are owed the duty too. | A heating system that leaves a home unfit to live in can be the basis of a claim long after installation. |
Most heating PI claims come back to three documents: the heat loss calculation, the system design and the estimate the customer saw before signing. Get those right and keep them, and most allegations can be answered.
The heat loss calculation. MIS 3005-D requires heat pump designers to calculate heat load using internal temperatures no lower than those in its Table 1 and external design temperatures from Table 2, both drawn from CIBSE guidance, and otherwise to follow BS EN 12831-1:2017. In a heat-pump-only system, the unit must provide at least 100% of that load at the chosen flow temperature without help from a supplementary electric heater; hybrid systems have their own rule. The standard also says that neither the building’s annual heat demand nor the system’s annual performance is appropriate for sizing.
Boiler sizing is changing too. The 2026 edition of Approved Document L, which takes effect on 24 March 2027 for building work other than higher-risk building work, says a room-by-room calculation should be used when installing a new heating system, and that sizing a replacement appliance from the output of the old one is not appropriate. Swapping like-for-like without a calculation will become harder to defend.
Flow temperature. Both Approved Document L and MIS 3005-D push designs towards 55°C or below. If you propose a heat pump design above 55°C, the standard requires you to offer an alternative at 55°C or lower and explain the difference in efficiency and energy use so the customer can choose. Record that choice.
The estimate. For homes, MCS requires a performance estimate using its standard method, given to the customer before the contract with a Key Facts sheet. You can add your own estimate, but it must explain its method, must not be more prominent than the MCS figure, and must warn the customer to treat it with caution if it is significantly better. Breaking those rules turns a sales document into evidence.
Permissions. MCS contractors must make customers aware of the permissions, approvals and licences the installation needs. Planning is the one most often missed.
| Usually covered by PI | Often excluded or limited | Needs a different policy |
|---|---|---|
| Negligent heat loss calculations and system sizing | Promises of specific running costs or savings, beyond reasonable skill and care | Gas escapes, fires and scalds during or after the work (public liability) |
| Design errors in emitters, pipework, controls and flow temperatures | Replacing equipment that failed mechanically | Carbon monoxide or other injury to your own staff (employers’ liability) |
| Incorrect advice on planning, permissions or the right system for the home | Redoing your own faulty workmanship | Faulty parts you supply that cause injury or damage (products liability) |
| Errors in grant or scheme paperwork handled for the customer, where the policy includes it | Fines or penalties imposed by a regulator | Tools, vans and stock (tools and motor cover) |
| Defence costs, including independent heating experts’ reports | Claims arising from circumstances you knew about before cover started | Breakdown of the customer’s own equipment (warranty or breakdown cover) |
Many heating businesses buy PL first and add PI later, often as a section of a combined policy. Check that the PI section describes heat pump design, heat loss calculations and grant administration if you do them, and that its limit is separate from the PL limit. The insurer’s acceptance and the policy terms decide what is covered.
No law sets a PI limit for heating engineers. Domestic customers rarely ask; housing providers, developers, landlords and commercial clients usually do, and their contract terms set the figure. For domestic work, base the limit on a realistic worst case: replacing your largest system, the customer’s extra energy costs and alternative heating, plus legal and expert fees.
PI is claims-made, so the policy that responds is the one in force when the complaint arrives. Heating shortfalls usually show up in the first hard winter, and running-cost disputes after a year or two of bills, so claims often come in well after you have been paid. If you retire, sell the business or stop designing heat pumps, arrange run-off cover. See run-off cover explained.
A complete proposal gets better terms than a bare one, and a broker can only present what you tell us. Have these ready:
Speak to a broker
PI for gas and heating engineers, placed by a named broker
Start the online proposal and save it as you go, or leave your number and a named broker will call you back, usually the same working day.
Apex Insurance Brokers is an independent insurance broker based in Bristol, established in 2009 and authorised and regulated by the Financial Conduct Authority. We are not tied to one insurer: we work with over 30 markets, including Lloyd’s syndicates through wholesale brokers, and every client has a named broker who handles the placement, mid-term changes, certificates for clients and the renewal.
If you only service and repair gas appliances, your main liabilities are injury and damage, which public liability covers. Once you size boilers, design systems, calculate heat loss or give running-cost estimates, you take on professional risk that public liability usually won’t meet. PI is usually the policy that responds.
No. The law requires Gas Safe registration for gas work, which is a registration, not insurance. Developers, housing providers and commercial clients often require PI in their contracts. If you hold MCS or other scheme certification, check that scheme’s own requirements as well.
It can, where the shortfall comes from your heat loss calculation, sizing or emitter design and the customer claims the cost of putting it right. PI doesn’t usually pay to replace equipment that fails mechanically or to redo faulty workmanship. Keep your calculations and design records for every job.
Possibly, if the customer relied on an estimate that was negligently prepared or presented as more certain than it was. MCS requires its standard estimate before contract, and any alternative must not be more prominent and must warn the customer to treat it with caution if it is significantly better.
Injury, explosion and fire damage are mainly public liability claims. PI may respond where a client alleges that negligent design or advice caused them financial loss, subject to the policy terms. Most heating businesses that design need both policies.
Your exposure is lower, but commissioning, control settings, flow temperatures and changes you make on site can still lead to claims. MCS separates design (MIS 3005-D) from installation (MIS 3005-I), so be clear which you are certified and contracted for.
Apex arranges professional indemnity insurance for gas and heating engineers across the UK. Tell us about your work and we’ll find cover that fits. Or call 0117 325 0027.
Start your PI proposal Call 0117 325 0027Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Registered in England and Wales, company number 07014570. This page is general information, not advice on your individual circumstances. Cover is always subject to the insurer’s acceptance and the policy terms, and this page does not guarantee that cover will be available or on what terms.
