Boiler Frequently Asked Questions

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Dunnd74 at en.wikipedia [CC-BY-SA-3.0 ( from Wikimedia Commons

Below we have hoped we can answer some questions you may have about boilers, the various types of boilers, and some information that may be helpful to you when choosing or having a boiler installed.

How can I tell how old my boiler is?
Unfortunately, there is no easy way to tell by simply looking at the boiler. You should have had records left when the boiler was installed though, so these can be checked to find out the age. If you have you’re boiler serviced with us you can check both the age and the efficiency with the registered heating engineer we send along.

How can I tell whether I have a regular or combination boiler?
If you have a combination boiler, you won’t have a hot water tank, over-tap electric water heaters or a cold water storage tank and the boiler will start up every time the hot tap is turned on. Another sign indicating a combination boiler is if it has five pipes (two for heating, two for hot water and one for gas) coming out of it.

How can I tell whether I already have a condensing boiler?
Look for the flue which will be sticking out though an external wall from the back of the boiler. If it is plastic and a white plume puffs out of it when the boiler is working then it is likely to be a condensing boiler. Non-condensing boilers will have a metal flue (because the gases are hotter) and except in cold weather, the gases will normally not be visible as they are much hotter than those from a condensing boiler.

Should I insulate first or replace my boiler?
If you have a poorly insulated home, then it is a good idea to insulate surfaces such as walls with cavity wall insulation and lofts with loft insulation, remember to also fully draught proof you’re home before installing a new boiler. A well insulated home should always require less heat, and if this is installed after boiler replacement it is likely that the boiler may be oversized – meaning that it won’t be working as efficiently and will have a higher upfront cost.

What size boiler will I need?
Boilers should be capable of providing heat for the number of radiators in the house, and the size of the property – oversizing will result in lower efficiencies and also large unnecessary capital costs. The size of boiler will depend on levels of the size of your home, how well it is insulated insulation of the home and the type of heating system you have.
For combi boilers, power rating is generally determined by hot water requirements as this will generally produce more than enough heat output for space heating. Size for size replacement is not recommended as insulation levels may have been improved or the original sizing may have been incorrect – heating and hot water demand should always be reassessed before any installation.

Can I replace my existing boiler with a non-condensing model if installing a condensing one is difficult?
There are some exceptions to the building regulations, where it is either impossible or unreasonably difficult/uneconomical to install a condensing boiler – these must be assessed and officially declared by a registered installer. In these cases the customer can still opt to install a condensing boiler but can apply for grants to subsidise the extra costs incurred.

Are condensing combi-boilers more efficient than regular condensing boilers?
Not necessarily. It is important to match your choice of system to your heating and hot water needs. A qualified installer can let you know which is most suitable.

Where should the flue for a condensing boiler be positioned?
Care should be taken not to position the flue where the plume can obstruct doorways, frequently used areas or neighbours. Minimum statutory distances between terminals and obstacles are set out in the building regulations – our installers will be able to refer you to these or feel free to call us. Also avoid positioning the flue above paths where condensate could drip down and freeze, causing damage/hazard.

Where should the condensate drain of a condensing boilers be positioned?
Suitable drain points include an internal stack pipe, a waste pipe, an external drain or gully or a purpose made soakaway. Internal drain points are preferable as less likely to become blocked by leaves or frozen condensate.

Are there any special ventilation requirements with a condensing boiler?
No – not for room-sealed balanced-flue appliances. Purpose made ventilation may be required if fitted in a compartment.

Can I fit my new boiler myself?
We strongly recommend that you should have your boiler fitted by a Gas Safe (formerly CORGI) or OFTEC registered installer, who will be registered under a competent persons’ scheme. If the boiler is not fitted by somebody registered under a competent persons’ scheme, you will need to apply to the local council who will check the installation and issue a completion certificate. *NB Since 1st April 2009, the gas installer registration scheme run by Corgi is no longer in force. The Health and Safety Executive have awarded the contract to Capita Group plc (Capita)

If I am replacing my boiler, is it okay for me to request that my installer leaves the controls as they were?
Not unless the existing controls are compliant with the current building regulations. All of Gas-Glow installers are fully aware of the requirements for potential controls upgrades to make their installation compliant with the regulations, and they will explain these to you.

How often should I service my boiler?
A boiler should be serviced once a year by a registered competent person. We recommend that you check with the manufacturer how often your particular boiler needs servicing, as some may need servicing more regularly than others. This typically costs between £50 and £75.

What is a system flush and do I need one?
When the boiler is replaced, it is important to make sure that the system is cleaned and treated. A clogged up system will not allow the full efficiency of the boiler to be met, meaning that more fuel will be needed to heat the home. This does not need to be performed annually, but is useful every few years. If you notice that the radiators are ‘cold spotting’, then it is probably time to have a system flush.

I’m not getting consistent heat from my radiators. What can I do?
If there are patches of radiators that are hotter or cooler than others, there are two things that you can do. Firstly, try ‘bleeding’ (see our guide here) the radiators yourself. If this does not solve the problem, then our registered heating engineer will be able to advise you as to whether a system flush and treatment will help. Please be aware that there are some treatments which may not be suitable for particular boilers, so always check with the manufacturer.