FAQs
New boiler installs: questions answered
Choosing, sizing, moving and paying for a new boiler.
New boiler installs
What affects the price of a new boiler?
The main factors are the boiler type and output, whether it is a like for like swap or a system conversion, moving the boiler or flue, gas pipe upgrades, controls, filters and cleaning the system. CombiCert's new boilers start from £1,750 inc VAT, confirmed after a site inspection of your home.
Should I get a combi or a system boiler?
A combi heats water on demand and suits most homes with one bathroom and good mains pressure. A system boiler with a hot water cylinder suits homes where two or more showers run at once, or where mains flow is weak. The right choice depends on your hot water use, so ask for an assessment first.
What size boiler, in kW, do I need?
For a combi, size is driven mainly by hot water flow, so homes with more showers need a higher output. For heating, the right figure comes from a room by room heat loss assessment, not the number of bedrooms. An oversized boiler costs more and can short cycle, so ask the installer how they worked out the output.
Which boiler brand is best: Worcester Bosch, Baxi, Ideal or Viessmann?
There is no single best brand for every home. Each makes reliable models, and the right one depends on output, size, controls and warranty terms. Installation quality and annual servicing matter as much as the badge. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann and repairs all major brands.
Can I swap my old tank system for a combi boiler?
Usually, yes. A conversion removes the hot water cylinder and loft tanks and fits a combi that heats water on demand. It needs more pipework than a straight swap, so it costs more and takes longer. Your mains water pressure and flow must be checked first, because a combi depends on them for hot water.
Can you take out a back boiler and fit a modern boiler?
Yes. Old back boilers behind a gas fire can be removed and replaced with a modern condensing boiler, often a combi, in a new position. The work includes removing the old appliance and cylinder if needed, new pipework and flue, and making the old gas supply safe. A site visit is needed to price it.
Can my boiler be moved to another room or into the loft?
Often it can, but moving a boiler adds gas, water and condensate pipework, a new flue position and sometimes electrics, so it costs more than a like for like swap. A loft boiler needs safe access, flooring and lighting. The installer must check the flue route and condensate drainage before confirming the new position.
How long does it take to fit a new boiler?
A straightforward replacement in the same position is usually done in a day. Moving the boiler, converting from a tank system or upgrading gas pipework can take two days or more. Your installer should confirm timings after the survey. See our boiler FAQs page for more on installation timescales in Telford.
Do I need a power flush before a new boiler is fitted?
Not always. The system should be cleaned so dirty water does not damage the new boiler, and manufacturers expect this for the warranty. That can be a chemical clean, a power flush or both, depending on the water's condition. A magnetic filter is normally fitted too. Ask what cleaning is included in your quote.
Is a free boiler under the ECO4 grant scheme legitimate?
ECO4 is a real government scheme delivered through energy suppliers, but cold calls using its name can be scams. Check eligibility on GOV.UK, never pay upfront, and confirm the installer is Gas Safe registered. CombiCert is not an ECO4 installer, but can advise on standard boiler replacement in Telford.
I am worried my new boiler was not fitted safely. What can I do?
Check the installer is on the Gas Safe Register and that you received the commissioning checklist and a Building Regulations compliance certificate, which the installer registers. Ask the installer to come back first. If you think the work is unsafe, contact Gas Safe Register, and stop using the boiler if you smell gas.
What is a powerflush?
A powerflush pumps water and cleaning chemicals through the heating system at high flow to lift sludge and scale out of radiators and pipes. It is often recommended before fitting a new boiler or when several radiators have cold bottoms. Afterwards, inhibitor and usually a magnetic filter are added.
What does a magnetic system filter do?
It is fitted on the return pipe to the boiler and catches magnetic iron debris before it reaches the boiler. An engineer cleans it out during servicing. Most manufacturers expect a filter and a cleaned, inhibited system for their warranty, so check your boiler's warranty terms.
What is the difference between a combi, system and regular boiler?
A combi heats water on demand from the mains with no cylinder or tanks. A system boiler heats a hot water cylinder and has pressurised heating parts built in. A regular or heat-only boiler works with a cylinder plus loft tanks. The right choice depends on your hot water demand and space.
What happens to my hot water cylinder if I get a combi?
It is drained and removed along with the cold water tanks in the loft, as a combi heats water directly from the mains. That frees cupboard and loft space. Old pipes left in place should be capped or removed correctly by the installer.
Can I keep my cylinder but get rid of the loft tanks?
Often yes. The heating can be converted to a sealed system with a filling loop, an expansion vessel and a pressure relief valve, and the cylinder can stay or be upgraded to an unvented cylinder. The heating tank is then no longer needed. An installer will check pipe condition first.
Will converting to a sealed system cause leaks?
Raising pressure can expose weak joints or old radiator valves that were fine at low pressure. A good installer pressure tests the system and fixes weak points during the work. Older systems may need a clean or some parts replacing first.
Does a new boiler need a filter and system clean?
Manufacturers usually expect the system to be cleaned and treated with inhibitor and a filter fitted when a new boiler goes in, and these steps affect warranty. Dirty water is one of the main reasons new boilers fail early. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann boilers around Telford and can talk you through the options.
Do I need to register a new boiler installation?
Yes. A Gas Safe registered installer notifies the installation to the local authority through the Gas Safe Register, and you should receive a Building Regulations compliance certificate. You should also register the warranty with the manufacturer. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann boilers around Telford and can talk you through the options.
Is my mains water good enough for a combi boiler?
Combi hot water depends on your incoming mains flow and pressure. An installer measures the flow rate at a cold tap before recommending a combi. Homes with low flow or several bathrooms used at once may suit a system boiler with a cylinder better.
What is an unvented hot water cylinder?
An unvented cylinder stores hot water at mains pressure without a cold tank in the loft, giving strong showers. It has safety valves and needs annual checks by a qualified person. It is often paired with a system boiler. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann boilers around Telford and can talk you through the options.
How do I make a warranty claim on my boiler?
Contact the manufacturer with the model, serial number, installation date and service records. They will usually send their own engineer or authorise a repair. Missing annual services can affect the claim, so keep records. Your installer can help with the details.
How do I know if my boiler is condensing?
Most gas boilers fitted in the UK since 2005 are condensing types. A plastic condensate pipe running to a drain, and a white plume from the flue, are signs. The data badge and manual will confirm. Condensing boilers are more efficient at lower return temperatures.
Can I box in my boiler?
You can, but leave the clearances the manufacturer specifies for servicing and ventilation, keep the controls accessible, and do not enclose the flue. Check the installation manual or ask your engineer before building a cupboard around it. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann boilers around Telford and can talk you through the options.
Does my heating need a bypass valve?
Many systems need a bypass so water can circulate when radiator valves and zone valves close, protecting the boiler. Combis often have one inside. The installation manual specifies when an external automatic bypass is needed. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann boilers around Telford and can talk you through the options.
How do I prepare for a boiler installation?
Clear access to the boiler, cylinder and loft if tanks are coming out, and plan for heating and hot water to be off during the work. Ask your installer how long it will take. CombiCert installs Baxi, Worcester Bosch, Ideal and Viessmann boilers around Telford and can talk you through the options.
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Need an engineer rather than an answer?
CombiCert Ltd, Gas Safe registered 621146, The Old School House, Park Lane, Telford, Shropshire TF3 4TG. Open Monday to Saturday 08:00 to 19:45, closed Sunday. Email hello@combicert.co.uk.
Smell gas? Call the National Gas Emergency Service on 0800 111 999.