Combi/Combination Boiler

The heating and hot water are combined into one as there is no hot water tank. Domestic Hot water is created at the time of need, and if the heating is currently on, it is temporarily turned off whilst hot water is delivered to the point of use. These are the most common boilers fitted over the last 20 years.

Conventional System Boilers

System boilers have a hot water tank (usually in an ‘airing’ cupboard) to store and deliver hot water to the baths and showers and sinks, and as such the heating can be run continuously. These are usually found in larger properties with 2 or more bathrooms.
Often, on older systems the water is supplied to the system from a cold water storage tank in the loft. As a result the system is typically running under gravity pressure. This is known as a Traditional Boiler.

CHP Boiler (Combined Heat & Power)

Relatively rare, these use gas energy to not only provide hot water and heating, but also to move a mechanical mechanism that generates electricity as well.

Hydrogen H2 Ready boilers.

The Government is actively encouraging boiler manufacturers to make their products Hydrogen ready for 2026. Hydrogen produces no CO2 when burnt, and so is part of their Net Zero strategy for 2050. These boilers will be designed to burn hydrogen rather than natural gas with a few simple part changes provided by a service engineer. Some H2 ready boilers are expected to be launched in 2022

If your boiler was installed in the last 20 years & you have no cylinder in a cupboard, then you almost certainly have a combi boiler.
If you have a hot water cylinder somewhere in the house, but no cold water header tank in the loft, then you have a system boiler.
Combi & System boilers account for 90% of all the gas central heating systems currently installed in the UK.

IS IT A CONDENSING BOILER?

Since 2005, all gas boilers (Combi & System) have to incorporate Condensing technology and is a requirement to achieve the ‘A’ rating. A condensing boiler captures the heat from the exhaust gases and recycles it to preheat the incoming water, thus reducing the overall energy consumed. In the process, water vapour in the exhaust gases is condensed creating a small amount of water that needs to be drained to waste usually through an outside wall. To identify this, look for a white pipe at the bottom of the boiler, typically 22mm in diameter.

TOP TIP: In a very cold weather snap the greatest cause of boiler call-outs is a frozen condensate waste pipe so check that first if your boiler indicates a fault condition

S IT 'A' RATED?

Most domestic appliances have an energy rating based on the efficiency. These rate from F to A with more recently A+ and even A++ ratings being introduced. All boilers from 2015 have to be A rated as a minimum; which is to say 90% energy efficient. A+ & A++ are 92% & 95% efficient respectively. If your boiler does not have an energy rated sticker then chances are your boiler is not A rated and you might want to consider a replacement.

As a rule of thumb, the CIPHE (Chartered Institute of Plumbing & Heating Engineers) recommend that your boiler is replaced every 10 years; but they would, wouldn’t they? Many manufacturers now offer typically 7 and sometimes 10 year warranties on their boilers so a lifespan of 10 years plus is easily achieved.

WHAT ABOUT THE MONEY?

Whilst an A rated boiler can save you around £200 per year compared to a G rated boiler in a 3 bed Semi-detached (source; energy saving trust) a boiler swap can cost between £1,500 & £2,000 so it can therefore take up to 10 years to recoup the cost of replacement if that is the only thing that concerns you.

SHOULD I SERVICE MY BOILER?

If your boiler is less than 20 years old, is reliable and you have it serviced every 2~3 years (every year by law if you are a landlord of a rented property) then there is no financial reason to swap out your boiler. If you have concerns about CO2 emissions, reliability in the winter, or if you are planning to sell your house (an older boiler will reduce the EPC rating of your property) then you might feel it appropriate to replace your boiler with an A or A+ rated appliance.

According to the energy saving trust, reducing the thermostat setting by 1°C can save an average of 10% (typically £60~£80 per year). By simply setting your rooms to 20°C rather than 21°C, you can make a big difference.

TURN IT DOWN!!!

If you turn you boiler down to, say, 65°C rather than the more usual 75°C then your boiler will run more efficiently, typically 3% better. This is because condensing boilers (see above) only condense when the water returning from your heating is 58°C or less (to create the cooling effect that causes condensing). If your return temperature is 60°C or more, your boiler won’t be condensing, it won’t be achieving the A efficiency rating and you won’t be maximising your energy savings. By having a lower flow temperature to start with you can practically guarantee that your return temperature will be below 58°C and so will be operating at maximum efficiency all the time.

When your boiler is serviced, your engineer will do a series of tests including of the flue gases, which indicate if the boiler is burning cleanly and thus efficiently. However, you may find that your radiators or skirting heating are not getting hot, and you may think this is because your boiler is faulty or needs replacing.

HANG ON! YOUR BOILER MIGHT BE JUST FINE...

MY RADIATORS AREN'T ALL GETTING HOT

If some radiators are getting warm and others not, chances are it’s trapped air and the problematic radiators need to be bled. More seriously it could be sludge in the pipework caused by the steel radiators rusting from the inside (skirting heating is usually made from aluminium so it won’t be rusting). This will require a flush to clean out the waste, and the system refilling with clean water and suitable rust inhibitor.

Skirting Heating is made from aluminium, so will not rust and sludge up your system

IS MY PIPE WORK PAST IT?

In really serious instances, the pipework itself may be past its sell by date (typically 40~50 years), and so replacing your boiler because your house is not heating up is not going to solve the problem.

Your heating engineer should be able to measure the pressure from and then the return to the boiler with all the radiators open and see if there is a significant pressure drop requiring remedial action.

Your system needs to be properly pressurised to work efficiently. This is typically 1.5~ 2.2 bar on the boiler pressure gauge (usually indicated by the green section on the gauge).
If your system continuously needs topping up (a boiler will usually go into fault mode if the pressure drops below 0.5bar) then you may have a leak somewhere on the system.
If you have a leak on a radiator or skirting heater, these are very easy to find and remedy- usually it will be where the pipework connects onto the radiator panel and simple to get at.

It is common in areas with high levels of calcium carbonate dissolved into the water, to use a water filter or softener to reduce limescale and improve the taste. Under no circumstances should chemically softened water be plumbed into the central heating system. Whilst limescale can build up in appliances that are constantly being refilled (such as kettles, baths etc) the water in the central heating is a ‘closed’ system and apart from the occasional top up (see above) the calcium carbonate levels are static. As such limescale build up is minimal in closed loop systems especially if plastic pipe has been used. Introducing chemically softened water can damage boilers, heat exchangers, aluminium radiators etc. and should be avoided at all costs. Mechanical or centrifugal filters do not present such a hazard, but double check the suitability of your heating system to accept softened water. If in doubt, treat only the domestic potable water.