We compare Boiler Magnetic Filters | System Cleaning Costs

Quick guide summary

Which are the best boiler magnetic filters? Why is a clean heating system important?

Magnetic filters for boilers are the modern method of keeping a central heating system clean. A clean system will lower heating bills and reduce maintenance costs. Dirty radiators cannot circulate heat effectively and will make the boiler work harder to heat the home, costing more in energy bills. A dirty system will eventually damage components of the system beyond repair. In this Guide, we help you identify if you have a dirty system and undertake a comparison of the best magnetic filter models from Sentinel, Fernox, Magnaclean and Worcester. For more guidance on cleaning your heating system visit our Guide to Power Flushing or Guide to Central Heating Systems and Boiler costs.

Overview of system cleaning

Best magnetic filters review

We compare 10 magnetic boiler filters from leading brands according to size, price and warranty to find the best filters.

System cleaning costs

Review typical product and labour costs for power flushing, magnetic filters and chemical treatments.

‘Sludge’ and ‘Grit’

Sludge and grit prevent your heating system from working properly. A dirty system makes the boiler work harder to heat the house and increases energy bills.

How to use this Guide

We review magnetic filters and costs

How does your system get dirty

what are the signs/effects of rust?

What is a Boiler Magnetic Filter?

Magnetic filters are a little device close to the boiler that keep your heating system clean long term. Heating water is always sent from the boiler around the radiators and back to the boiler again. The magnetic filter is fitted on pipe that returns water back to the boiler. As water passes through the device, a large magnet attracts any rust out of the water onto the magnet so that only clean water is passed back to the boiler. The filter will need to be cleaned out once a year or so.

They are very commonly installed as part of a new boiler installation and some manufacturers will extend their boiler warranty period when they are fitted at the same time. NB for a heavily blocked system a magnetic filter alone will not be enough to clean it, you will need to power flush the system first (for more see our Guide to Power Flushing). A magnetic boiler filter will be able to keep it clean after the power flush

We Review Magnetic Filters by Brand

We have reviewed 10 models of magnetic filter by price, size, warranty and function. All filters do broadly the same thing, which is to pull magnetic and non-magnetic dirt out of the system. Some have developed their filtration systems more than others however.

We have separated the filters into two groups by warranty period. The first group contains filters with a warranty of 8 years or more. The second group contains filters with a warranty of 2-5 years.

We have identified a ‘best buy’ in each group, which we think provides a great all round product in terms of technology, price and warranty period. Speak to your fitter about your preferred choice and why. NB check the height you have available to fit the filter.

Top Tip : work out available space for the filter

It is very common for space to be restricted when fitting a magnetic filter. Our tables below show the height of each filter. If you are restricted on space pick one of the compact models. NB you must leave room for servicing. Check the manufacturers instructions for how much room to leave to be able to clean on the filter.

Magnetic Filters with 8 + years warranty

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Make Magnaclean Magnaclean Sentinel Fernox Worcester
Model Micro 2 Professional 2 Vortex 300 Omega Filter Greenstar Filter
Price £83.50 £93.50 £90.00 £77.00 £127.00
Height 151mm 203mm 205mm 209mm 279mm
Technology Standard filter Standard filter Vortex (Screw) - slows down water to improve retention Standard filter Slows water down to improve retention of rust
Debris removed: Magnetic
Non magnetic
​Non magnetic
​Non magnetic
​Non magnetic
​Non magnetic
Warranty 10 years 10 years 10 years 25 years 8-10 years with new Worcester boiler

Magnetic Filters with a 2-5 year warranty

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Make Fernox Altecnic Grant Sentinal Fernox
Model TF1 Compact Dirtmag IQ Vortex Eliminator TF1
Price £72.00 £78.00 £95.00 £49.00 £78.00
Height 192mm 238mm 243mm 251mm 288mm
Technology Cyclone Water hits internal mesh and drops to bottom or attracts to magnetic if rust Standard filter Cyclone - 'spins down' particals to bottom of collection chamber Cyclone - 'spins down' particals to bottom of collection chamber
Debris removed: Magnetic
Non magnetic
​Non magnetic
​Non magnetic
​Non magnetic
​Non magnetic
Warranty 2 years 5 years 2 years 2 years 2 years

System Cleaning Costs

There are a number of very effective measures available to clean your system and keep it clean. The best measures are always preventative, i.e. adding a chemical called inhibitor and using a magnetic filter. Other measures such as power flushing will reverse a built up of dirt in the system but will not reverse any damage it may have caused. The table below give a breakdown of approximate costs for stand alone system cleaning measures. NB if for example you have a magnetic filter or powerflush with a new boiler installation then the labour charges will likely be reduced to reflect the other works being undertaken at the same time.

Work undertaken Approximate costs< Time

Stand alone powerflush using dedicated flushing machine

• £500-£600 incl VAT 6-10 radiators.
• £600-£750 incl VAT 11-15 radiators.

• 1-1.5 days (or a long day)

Work undertaken Approximate costs Time

Stand alone chemical cleanse - add strong chemical to the system, leave a few hours/days, drain down and refill with clean water and inhibitor

• £380 incl VAT 6-10 radiators.
• £420 incl VAT 11-15 radiators

• Half day

Work undertaken Approximate costs Time

Magnetic filters

• £70 incl VAT per hour.
• Cost of filter varies according to the product (see product tables and prices below)

• 1-2 hours

Work undertaken Approximate costs Time

Adding Inhibitor (should be done after every drain down and fro all new boiler installations

• £70 incl VAT per hour.

• 1 hour

What are the signs and effects of rust?

‘Sludge’ and ‘Grit’ in the system

‘Sludge’ is a common industry term for a build-up of rust in the system. Sludge builds up in open vented system. A harder form of debris forms in sealed systems, which we refer to as ‘grit’.

Signs of rust in the system

The effects of sludge and grit vary. Sludge tends to lead to cold spots at the bottom of radiators, as the rust settles at the bottom in little piles.

Grit tends to affect system components in the boiler and system, such as the heat exchanger (you will experience only warm water) or the pump (which will eventually seize).

Where the system is heavily affected by sludge or grit, the components, and sometimes the radiators, will need replacing and the system ‘powerflushed’.

How does your system get dirty?

A lack of ‘Inhibitor’…

All water based heating systems must contain a percentage of a chemical called ‘inhibitor’. Inhibitor is a chemical mix that prevents corrosion and bacterial growth. The life span of inhibitor varies between products, but in any event if the system is drained for maintenance inhibitor must always be added back when the system is re-filled with water.

If at any point inhibitor has not been added to the system then, over time, the pipes and radiators will begin to corrode and a build-up of rust will occur.

Cleaning and prevention

When a system is heavily affected by sludge or grit, sometimes the only way to properly clean it is to ‘power flush’ it. This is usually a day’s work and costs can range between £450 and £750. An alternative where the system is less dirty is a ‘chemical cleanse’.

What is a power flush?

A powerflush is a means of thoroughly cleaning the pipe and radiators in a heating system. A cleaning solution is pumped through the system and breaks down the rust build up. The rust particles are then captured by a magnetic filter attached to the machine.

Whilst flushing, all radiators are turned off and one opened at a time in order to focus that machine on that section. Each radiator is turned on one at a time until all the radiators are done.

After cleaning, the system is refilled with water and inhibitor is added.

My boiler cover provider has told me to have a power flush

If you have called out your boiler cover provider to a fault they have deemed to have been caused by rust, then they will replace the faulty parts but it will be conditional on you having a power flush. They are likely to insist this is done before they fit new parts.

Radiator Flush with a Chemical Cleanse

A strong chemical is added to the system and left in for a period of hours or days, depending on the strength of the chemical. The chemical will break down the rust over that period. The system is then drained down, radiators flushed and refilled with clean water and inhibitor added. If the system is heavily rusted then this may not be sufficient and a power flush will be required.

What would you like to do next?

Use our calculator to get an estimate of boiler installation cost


When to Repair or Replace your boilers


Advice on Water Pressure and ‘flow rates’


More useful guides

Book a survey with a local heating company


Guide to Power Flushing


Guide to Heating Controls