08 Oct 2021

By Phil Turtle, Compliance Director at Landlord Licensing & Defence

“Winter drawers on!” was the risqué chorus amongst the women on the shop-floor where I served my engineering apprenticeship, every year, as the weather started getting colder!

And that reminded me that it’s time all landlords were making sure their boilers are going to withstand the onset of winter – without the annual breakdowns that are so common, and which leave tenants in the cold and landlords open to prosecution and fines by Councils.

Viessmann-trained installer, Paul Spence, conducting a full boiler service in Leeds. All key components of the boiler are inspected and cleaned.

Gas Safety Check is Not Enough

Most landlords do not understand that a Gas Safety Check does NOT include a boiler service, and therefore they are leaving their boiler un-serviced year, after year, after year. This leaves them at significantly higher risk of inefficient operation and winter breakdowns.

Many annual ‘servicing’ packages only include the gas safety check but the proper maintenance of a full annual boiler service is essential for boilers to run safely and efficiently.

It is well worth knowing the difference – to maximise your rental property’s heating comfort, minimise your energy bills, have dependable heating without breakdowns, and extend your boiler’s life.

Gas Safety Check

A gas safety check takes basic precautions to ensure that your boiler and it’s pipework do not have any potentially dangerous faults. This is primarily to safeguard against potentially explosive gas leaks and to prevent the production of odourless, but deadly, carbon monoxide gas. Carbon monoxide can be produced if a gas appliance has been improperly fitted or repaired, or if it has been inadequately maintained. Carbon monoxide can also accumulate if there are blockages in vents, flues or chimneys.

A gas safety check only confirms that the boiler is properly set and adjusted, so that the gas burns correctly; is suitable for the room in which it is located; is physically stable, securely fitted and properly connected to the gas pipework: has an adequate and permanent air supply.

A gas safety check should also confirm that all safety devices are functioning properly and that any flues, chimneys and air vents are operating correctly. The heating engineer will insert a flue gas analyser probe into the sampling points (for air in and air out) in the flue, just above the boiler, and check that the emissions are within the legal parameters.  

Gas safety checks must be conducted by an engineer who is Gas Safe-registered. Such a check will typically take no more than 15 to 20 minutes.

Boiler Full Service

A boiler service should also be undertaken by a Gas Safe registered engineer, (and you should check that his/her Gas Safe registration includes boiler servicing as not all Gas Safe engineers are qualified to also service boilers). Ideally you should choose an engineer who is accredited by your boiler manufacturer. Most manufacturers publish detail of these on their websites.

In addition to gas safety this provides a full list of other important checks, a deep clean and whatever is necessary to keep the boiler performing well. This is crucial, because the inside of a boiler is such a tough working environment – flowing water and fierce heat!

If we look at in that other hot and hostile environment we all know well, our car engine, we know well that some mechanical parts need to be regularly cleaned and adjusted and replaced before they suffer mechanical or functional failure.  By analogy the Gas safe check is the MoT, and the boiler service is the 6,000-mile full service.

Only the foolish motorist doesn’t service their car and its engine. Why then do landlords see it as acceptable not to service the boilers in their rental properties?

Especially as most landlords know how excruciating a problem it is when an un-serviced boiler fails, when they are under most strain, in the depths of winter.

Leaving tenants without heating and hot water for days on end and making complaints to the council when you, the landlord can’t find a gas engineer or, even if they can find one, the parts have to be ordered.

What Could Possibly Go Wrong?

I asked Andrew Lambert, area service manager at boiler manufacturer Viessmann, to tell me what goes wrong when landlords fail to service their boilers annually and why so many landlords have winter boiler problems.

Andrew explained: “If a boiler is repeatedly not serviced correctly then the following issues will begin to occur with greater effect year on year:

Expansion vessel pressure  – If the vessel is not checked and recharged each year, based on average use of a system it will start to create a problem around the 3-4 year mark.

By 4-years old, the average system, if not maintained correctly, begins to start showing problems with system pressure increasing above 3bar, causing the pressure relief valve to discharge, which can struggle to reseal, resulting in ‘low pressure’ when the system is static.

Most people will notice they are topping up the boiler more regularly. Tenants will often not alert the landlord. The more water you fill a system with, the greater the likelihood of corrosion caused by the oxygen content of the fresh water.

It is essential in modern sealed systems, especially combination boilers, that expansion vessel pressure is tested and maintained to keep the system from the cycle of discharge and refill.

Carbon soot deposits in the combustion chamber – Is a natural by-product of the combustion process and can be found lying around the main heat exchanger.

If this is not removed and cleaned every year nuisance blockages will occur in the condensate siphon. It will reduce the efficiency of heat transfer from the burner into the main heat exchanger.

When a burner has not been opened up and cleaned regularly, after 6-7 years it will certainly begin to increase the chamber pressure, as the heat is disappearing up the chimney rather than being transferred into the main heat exchanger.

Ultimately, a reduction in burner output means heating your hot water takes longer, and in serious cases will fail to reach the specified temperature.

The end-game for this scenario is failed ignition.

Ignition/ionisation probes – Failure to have these regularly cleaned and checked can result in explosive ignition, or failed ignition.

The ionisation probe measures the current generated by combustion. It can become coated overtime and result in lower ionisation current, which will eventually result in a failure at the flame stabilisation safety check.

Frustratingly for the end-user, the combustion can be in good condition but if the probe measuring its safety has been left to degrade it will start to shut down the burner as a safety measure – leaving tenants in the cold.

Hydraulics – Although it is not part of a standard service on a combination boiler we instruct our service technicians to start by running the hot water at the specified flow rate. They are then looking to see how the hydraulics flow through the secondary heat exchanger.

If the main flow temperature is rising above approx. 80C, we know there must be resistance in flow caused by blockage of the system water and then the compromised components can be repaired or replaced, keeping the boiler healthy and operational through the winter.”

Cost Versus Risk

The very real risk of not having boilers serviced is not only tenants without heating and hot water, but also the cost of emergency plumbers and emergency spare parts. Worse still is that tenants involve the council, and they issue massive fines to the landlord.

Particularly dangerous if you’re an HMO landlord when the council can issue an immediate fine of up to £30,000 under the HMO Management Regulations 2006.

The modest cost of this maintenance work is far preferable! Having a full boiler service once year will prevent most inconvenience. 

Leeds-based Viessmann-trained installer, Paul Spence (pictured), says it’s imperative to be meticulous with a boiler servicing regime, and warns landlords: “ If your boiler engineers are not on-site for at least 60 to 90 minutes, then your boiler can’t have been fully serviced.”

Only by booking a full service every year will you ensure that your boiler performs as efficiently as it can for as many years as it should.’


Landlords are only just starting to understand that the fines for non-compliance on all matters to do with housing health and safety, plus management regulations, are eye-watering. Often 20% or more of the value of the property. 

Find out how to obtain an MoT of your property’s compliance status, to enable you to avoid Council Enforcement here:  Compliance Audit

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