New boiler installations
Power Flush Before a New Boiler Installation
A new boiler deserves clean water. Here’s why the system should be cleaned before a new boiler goes on, what the standards and manufacturers expect, and how a power flush helps.
Why system cleanliness matters for a new boiler
When you replace a boiler, the radiators and most of the pipework usually stay. That means the water — and whatever debris is in it — stays too. If the old system is full of magnetite, sludge and scale, the new boiler starts life circulating that dirt.
Modern condensing boilers are efficient partly because their heat exchangers have narrow, finely shaped waterways. That design is also why they’re more sensitive to debris than older, simpler boilers. Blockages can cause overheating, noise, reduced output and early failure.
assets/img/photos/new-boiler-installation-clean-system.webpWhat the standards say
BS 7593 is the British Standard code of practice for the treatment of water in domestic hot water central heating systems. It sets out that heating systems should be cleaned, flushed and protected with inhibitor when a new boiler is fitted, with a filter also commonly recommended.
Building Regulations guidance for England (the Domestic Building Services Compliance Guide) refers to cleaning and treating systems in line with BS 7593, and boiler manufacturers’ installation instructions typically require the system to be cleaned before the boiler is connected.
Check your warranty terms. Many boiler manufacturers require the system to be cleaned and treated — and some require a filter — for their extended warranty to apply. If a heat exchanger fails due to debris, a claim can be refused.
Do you need a full power flush?
The requirement is that the system is cleaned. The appropriate method depends on its condition:
- Light contamination: a chemical clean followed by a thorough flush may be enough.
- Moderate to heavy contamination — black water, cold-bottomed radiators, visible sludge: a power flush is usually the most effective method, because it can clear settled sludge that a chemical clean alone won’t shift.
- Very old or fragile systems: sometimes it’s better to replace the worst radiators alongside the boiler, and clean the rest. We’ll tell you honestly.
More on the differences in power flush vs chemical flush.
How we fit in with your boiler installation
Check the system
We assess contamination and system condition, ideally before the installation date.
Flush before the new boiler goes on
Where possible we flush using the existing boiler or with the new boiler isolated, so debris never passes through the new heat exchanger.
Clean water, ready for the installer
Every radiator is flushed and the system refilled with clean water.
Inhibitor and filter
Inhibitor dosed to the correct level, and a magnetic filter fitted or recommended to protect the new boiler long-term.
If you’re having your boiler replaced by our sister company, London Safe Gas, we can coordinate the flush and installation. We’re also happy to work alongside any other installer.
Signs your system should be flushed before a boiler replacement
- The old boiler failed with a blocked or damaged heat exchanger
- Black water when bleeding radiators
- Radiators cold at the bottom
- The old boiler was noisy or kettling
- No record of the system ever being cleaned or treated
New boiler power flush questions
Do I need a power flush with a new boiler?
The system must be cleaned before a new boiler is connected — that’s the expectation in BS 7593 and in most manufacturers’ installation instructions. Whether that cleaning needs to be a full power flush depends on how dirty the system is. On older systems with sludge, a power flush is usually the most effective method.
Will my boiler warranty be affected if the system isn’t cleaned?
Many manufacturers make system cleaning, inhibitor and often a filter a condition of their warranty, and may refuse a claim if the heat exchanger is damaged by debris. Check the terms for the specific boiler you’re having fitted.
Should the flush happen before or after the new boiler is fitted?
It can be done either way depending on the installation. Many engineers flush the system on the old boiler (or with the new boiler isolated) so debris never passes through the new heat exchanger. We can coordinate with your installer.
My installer says the system will get a “flush”. Is that the same?
Not necessarily. It might be a chemical clean, a mains-pressure flush or a full power flush. Ask which method, and whether each radiator will be flushed individually.
Can you power flush if another company is fitting my boiler?
Yes. We can flush the system ahead of the installation date and leave it clean and treated for your installer.
Protect your new boiler
Let us clean the system before your new boiler goes on — or work alongside your installer.