What happens during a free boiler survey

What does an engineer actually do during a boiler survey?

A boiler survey is an assessment of the property, not a repair visit. The engineer starts with the boiler you already have: make, model, position and the space around it. The rest of the system is then looked at, because a new boiler has to work with the pipework and radiators that are already in the house.

• the existing boiler, where it sits and how much clear space surrounds it
• the flue route and where it ends on the outside wall or roof
• the gas supply and the pipework feeding the appliance
• the radiators: how many, what size and which rooms never warm up
• hot water demand: bathrooms, showers and taps that run at the same time
• the controls you use now — room thermostat, programmer and radiator valves
• mains water pressure and flow, which matter most where a cylinder is involved
• where the condensate pipe can reach a drain

How does the engineer work out what size boiler your home needs?

Boiler size comes from a heat loss calculation, not from the number of bedrooms. The calculation takes in floor area, the number of radiators, the number and type of windows and the insulation. It works out how much heat the house loses on the coldest day of the year. Output is measured in kilowatts, and domestic boilers commonly sit between about 5 kW and 35 kW.

Oversizing is the old mistake. Boilers were once fitted up to 30% larger than the home needed, which wastes energy rather than adding comfort. The survey also settles the type of boiler. A combi heats water straight from the mains on demand and needs no cylinder, while a system boiler works with a cylinder and can serve several outlets at once.

Combis generally suit homes with one bathroom. Two bathrooms in regular use usually point towards a system or heat-only boiler, as our guide on combi, system or regular boilers explains.

What does the survey check about the flue and the condensate pipe?

Flue position decides whether a boiler can stay where it is. The flue is the pipe that carries combustion gases and excess heat safely out of the building. Manufacturer flue guides set minimum clearances, and the engineer measures them on site. Ideal Heating's flue guide gives 2.1 m above ground level where the terminal sits over a public or frequently used path. Another example is 300 mm from an openable window or air vent. Boilers with a higher output can need larger clearances.

Condensate drainage is the second fixed point. A condensing boiler produces acidic waste water that has to reach a drain. Worcester Bosch guidance allows an external condensate run of no more than 3 m and requires it to be insulated, because an uninsulated pipe can freeze. Drainage is the main reason boilers usually sit in kitchens, utility rooms and bathrooms. Viessmann guidance also notes around 60 cm of clear space in front of the boiler for servicing access.

What should you have ready before the boiler survey?

Have the details of your current system to hand. Many survey questions are about how you use heating and hot water, and only you can answer those.

• the make and model of the existing boiler, plus any manuals or paperwork
• the last service record or gas safety record, if you have one
• the reading on the boiler pressure gauge — cold, this is typically 1 to 1.5 bar, though the exact figure is set by the manufacturer
• how many radiators you have, and which rooms stay cold
• how many bathrooms and showers, and whether two ever run at the same time
• which room thermostat and programmer you use now
• access to the boiler, the loft, the cupboards and the outside wall
• for landlords: your existing gas safety records, which must be kept for two years

Safe checks you can make yourself are limited to four things: the pressure gauge, the thermostat and programmer settings, the reset button and bleeding radiators. Our guide on low boiler pressure explains what the gauge is telling you. Anything touching gas, the flue or the inside of the boiler case is work for a Gas Safe registered engineer.

Why does a boiler survey look at water quality and system filters?

System cleanliness decides whether the manufacturer warranty holds. BS 7593:2019, the code of practice for commissioning and maintaining domestic heating systems, requires an inhibitor in every wet central heating system. Baxi's guidance is to fit a filter, dose the inhibitor, clean the filter at each annual service and redose every five years or after work on the system.

Warranty terms follow the same logic. Baxi states that a magnetic filter must be fitted and maintained throughout the warranty period, otherwise a shorter warranty applies. A missing flush or inhibitor can invalidate cover. The engineer therefore looks at radiator condition and at signs of sludge during the survey. Our guide on power flush or chemical flush covers how the two cleaning methods differ.

Which rules in England does a new boiler have to meet?

Three sets of rules shape what a boiler survey in England can lead to. Gas work may only be carried out by a business on the Gas Safe Register, under the Gas Safety (Installation and Use) Regulations 1998 as amended.

• Boiler Plus (England, since April 2018): every new gas or oil boiler in an existing home needs time and temperature control plus a boiler interlock
• gas boilers in existing homes must meet a minimum ErP efficiency of 92%
• gas combi boilers need one extra measure as well: smart controls, weather compensation or load compensation
• Building Regulations: replacing a boiler is notifiable work, so the local authority has to be told

An installer registered with a competent person scheme can self-certify the work. The scheme notifies the local authority and a certificate is issued within eight weeks of completion. The completion certificate matters later, because solicitors ask for it when the house is sold.

What happens after the boiler survey with FM Power?

FM Power carries out a free home survey before a new installation. A written fixed price follows before any work starts. Brands fitted include Worcester Bosch, Vaillant, Ideal, Baxi, Glow-worm, Viessmann and Megaflo.

• the old boiler is taken away
• the manufacturer warranty is registered for you
• for landlords, the gas safety record (CP12) is sent by email the same day
• there is no monthly contract

FM Power is Gas Safe registered and covers London and the surrounding counties, seven days a week including evenings and weekends. If a replacement is on your mind, the new boiler installation page sets out what the work covers.

Sources

• Gas Safe Register — HSE
• The Gas Safety (Installation and Use) Regulations 1998, regulation 36
• Gas safety check records and what to keep — HSE
• Gas safety — carbon monoxide awareness FAQs — HSE
• Building regulations approval: use a competent person scheme — GOV.UK
• Boiler Plus: new standards for domestic boiler installations from April 2018
• What size boiler do I need for my home? — Viessmann UK
• Flue guide — Ideal Heating
• Does an external condensate pipe have to be insulated? — Worcester Bosch
• Boiler warranty information — Baxi