Composite under boiler system filter with a brass manifold designed for easy installation in small, restricted areas and with concealed pipework. This high-performance filter can be installed directly under the boiler or in restricted spaces due to the compact, versatile design. The TF1 Sigma UB Filter offers the ultimate in installer choice and provides high efficiency protection against the build-up of system debris.

  • A high capacity, compact design
  • Ideal for use in restricted spaces
  • Integrated three way valve with filter isolation and cleaning functionality
  • Durable and robust construction, made from a high-quality glass reinforced engineering polymer, and non-porous forged brass
  • Will not block or restrict flow
  • Can replace return valve if required
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Product Overview

The TF1 Sigma UB Filter body is constructed from a high strength engineering grade polymer, suitable for heating and cooling system applications. The glass reinforced polymer has good hydrolysis resistance, as well as high resistance to strain and abrasion. The polymer is compatible with glycols and additives used in central heating systems. The filter manifold is constructed from a premium grade, non-porous forged brass, allowing for direct connections onto the system, and a simple servicing procedure via the precision engineered manifold.
The TF1 Sigma UB Filter has been designed to ensure there is minimal pressure loss in addition to maintaining a high collection efficiency. The filter has been designed to capture a range of system contaminates, whilst also ensuring it cannot block, reduce flow through pipework or impact the performance of the heating system.
The TF1 Sigma UB Filter utilises a range of high-quality component parts that ensure the filter offers optimum performance. The three-way ball valve has been designed to allow users to easily operate by hand, whilst also providing a reliable serving procedure. The filter manifold includes a secure connection to the system and a robust service point allowing the filter to be drained and cleaned. The magnet is made using premium grade neodymium, enabling a high efficiency capture rate, as well as a robust filtration medium that will ensure a continued and consistent level of collection

Application, Fitting & Dosing

Designed to be installed close to the wall, the filter can be easily fitted under boilers and in all other areas where space is limited. The TF1 Sigma UB Filter can be installed under a boiler or in tight and restricted areas. Ideally the filter should be fitted on the return to the boiler and should be installed horizontally. To enable the TF1 Sigma UB Filter to be connected to the boiler and/or return flow pipes, separate flexible/corrugated pipes and/or adapters may be required (not supplied).

The TF1 Sigma Filter is designed to protect the boiler from the damaging effects of circulating corrosion debris, which has collected in the system as a result of a chemical reaction when water comes into contact with mixed metals used within a heating and cooling system. Treating the system with a quality inhibitor product from the Fernox Protector range will prevent the formation of sludge and scale long term in accordance with regulations and best practice.

Package, Handling & Safety

As with all magnetic products, if you have an implanted cardiac device extra caution should always be taken when handling any magnetic filter.
Individually packaged with instructions included. No special storage requirements.


Suitable Fluids:
Inhibited Glycol Solutions
Fernox Chemical Range / System Additives
Maximum Percentage of Glycol – 50%

Maximum Working Pressure – 5 bar
Maximum flow rate – 40 L/min
Maximum Working Temperature – 100⁰C
Capture Rate – Up to 100% of system contaminates

Operating Principle
– Contaminated water enters the filter via the brass manifold, carrying system debris and particulate matter held in suspension. This debris, including ferrous impurities such as Magnetite, moves through the manifold and into the main body of the filter.

The dynamic flow created within the filter means dirty water is transferred directly to the central magnet assembly. The high-powered neodymium magnet is designed to capture and retain large quantities system debris, protecting the boiler and helping to prevent breakdown and costly repairs.

The engineered flow path within the filter reduces magnet wash-off and improves the pressure loss across the filter assembly, meaning the filter can capture the maximum amount of debris, whilst causing no restriction to flow.

Water is directed to pass over the magnet sheath before exiting via the manifold. As a result, system debris cannot escape from the filter and is either trapped in the area of low flow, or captured by the powerful neodymium magnet, to allow clean water to exit the filter.

The filter utilises a precision engineered three-way valve, meaning any dirt collected within the filter can be quickly discharged via the drain valve by simply removing the magnet from the sheath, and turning the valve handle to engage the service function and open the drain valve, at which point system debris will be flushed from the filter and removed from the system. This procedure is shown in the cleaning guide

Physical Specification / Properties

Filter Body – Glass filled, engineering polymer
Manifold – Nickel plated brass
Seals & Washers – EPDM

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Product Code
Single Unit Dimensions(Height x Width x Depth)
Single Unit Barcode
Outer Carton Dimensions(Height x Width x Depth)
Outer Carton Barcode (ITF)
40 × 185 × 40 mm
90 x 221 x 200 mm
With Valves
112 × 346 × 179 mm
240 x 368 x 354 mm
With Valves
112 × 346 × 179 mm
240 x 368 x 354 mm
Slip Socket
70 × 190 × 132 mm
160 x 270 x 200 mm
Dimensions Diagram

Boiler noise is usually the result of limescale deposition within the heat exchanger of a boiler. This condition is worsened if magnetite is also present in the system, as this combines with the limescale to form a much harder deposit.

Boiler noise is usually the result of limescale deposition within the heat exchanger of a boiler. This condition is worsened if magnetite is also present in the system, as this combines with the limescale to form a much harder deposit. Other sediment forming debris such as sand and brick dust entering the system during installation can also become part of the hardened deposit. Local water conditions also play an important part, particularly the scale-forming solids dissolved in the supply water.

Boiler noise is directly related to the rapid condensation or implosion of steam in water. Localised boiling develops on the surface of the deposit, and small steam bubbles are created that make a rattling noise as they leave the surface and travel around the system.

When installed into existing systems, new boilers can become excessively fouled soon afterwards by oxide sludge present in the system water. Replacing a boiler can disturb soft sludge and loosen sediment in other parts of the system, causing these contaminants to be transported by the system water and re-deposited in the new heat exchanger.

The same phenomenon can occur as a result of circulator replacement if flow rates change. The risk of sediment and sludge deposition in new boilers can be avoided by cleaning the system as part of the installation process. Guidance on correct cleaning and treatment can be found in BS 7593:2006 Code of Practice for Treatment of Water in Domestic Hot Water Central Heating Systems.

What should be done?

Fernox Boiler Noise Silencer F2 is specifically formulated to significantly reduce boiler noise by reducing the surface tension of the system water. The reduced surface tension prevents large bubbles from being able to form and so the associated noise is greatly lessened.  Fernox Boiler Noise Silencer F2 efficiently treats the effects of a noisy boiler until the causes can be treated with a full clean of the system.

Fernox DS40 Descaler and Cleaner selectively dissolves scale deposits without attacking the metals commonly found in central heating s62486ystems. However this acid-based cleaner should only be used in new installations or in systems less than 10 years old.

Older systems that have been untreated for periods of time may have existing leaks that are temporarily plugged with corrosion debris. Installations with a history of radiator corrosion failures should not be acid cleansed, as other radiators are likely to have deep corrosion pits or complete perforations.

Older installations can be substantially improved, however, by dispersing the sludge with Fernox Cleaner F3 or Fernox Fernox Powerflushing Cleaner F5, followed by powerflushing with plain water.

After removing all soft sludge from older installations, separate boiler de-scaling may be helpful to resolve the problem. In order to do this, all the radiators should be isolated after which the system can be descaled with Fernox DS40 System Cleaner over a period of time – up to 24 hours.  This process should be followed by neutralisation with Fernox System Neutraliser before powerflushing with plain water.

Fernox Cleaner  F3 should ideally circulate around the system for at least one hour, or up to a week, after which it should be drained out and the system flushed/ cleaned before adding Fernox Protector F1 or Protector + Filter Fluid together with a Fernox TF1 Filter to protect the system from further corrosion and scale formation.

The Fernox Express Inhibitor Test is available from all major merchants and online plumbing retailers.

BS 7593:2019 recommends that the inhibitor should either be re-dosed at 5-year intervals or, a more comprehensive laboratory test is conducted every five years to provide a more in-depth analysis, and where needed, establish targeted action to resolve issues and restore system efficiency. The Fernox Water Quality Test includes everything needed to take a sample of the system water and send it off to the Fernox laboratory for full analysis.

It’s easy to keep track of test results with the free to download Fernox Water Test App, which installers can use to manage and evidence each test. Using the in-app camera, users take a picture of the test strip and select its colour to generate the pass or fail result. Using this process will auto-generate a PDF certificate with the result to your email address and this acts as evidence that the test has been completed and the system is fully protected. For ease, all of your submissions will be stored in your account for you to view and export on demand. If a test fails, installers can also demonstrate that action has been taken and the system subsequently re-tested to receive a positive result.

With the initial dose, its key to make sure the system water is circulated properly so that the inhibitor is sufficiently mixed. Fernox recommend that you let the system circulate for at least 15 minutes. Also having the system on hot will help speed this up.

If the dip test shows less than 100ppm, installers can immediately resolve the issue by adding a high-quality inhibitor such as Fernox Protector F1 or where a filter is fitted, Protector+ Filter Fluid. The test can be re-taken once the inhibitor has circulated to confirm the level has been met.

The results are instant!

Yes! the Express Inhibitor Test is a universal test that will check for the presence of all molybdate based inhibitors within the system water.

Simply dip the test strip into the system water and it will instantly change colour. By comparing the test strip to the colour chart label on the bottle, installers can assess whether the system water includes the correct concentration of inhibitor. A fully protected system will have inhibitor levels of 100ppm or above – and will pass the test. However, if the test fails and a result of less than 100ppm is received, the system should be re-dosed.

A core requirement under BS 7593:2019 is that central heating systems are tested annually, to help maintain system health and to identify and rectify any issues before they cause damage to the system. The Benchmark Commissioning Checklist further supports this practice to evidence the correct servicing and installation of boilers. The onsite Express Inhibitor Test makes compliance with these industry standards easy.

It is an easy to use dip strip that tests central heating systems for the correct concentration of inhibitor, to ensure that the system is fully protected and sludge and debris is prevented from forming and building up.

Yes, all Fernox internal leak sealers, such as Fernox Leak Sealer F4, are safe for use with combination and other low water content boilers.

They will not block valves or vents. Leak Sealer F4 Express is recommended for all pressurised systems as this can be added in 30 seconds via a radiator, filling loop or Fernox TF1 Filter, without the need to drain the system.

Disinfection is a process which destroys or irreversibly inactivates micro-organisms, reducing their numbers to a safe level.

Its purpose is to leave a clean water supply. It must be carried out in the following circumstances:

  • During routine annual system maintenance
  • New installations n After major system extensions or alterations
  • After installing underground pipework, except localised repairs which require prior disinfection of components
  • Where it is suspected that contamination may have occurred: i.e. fouling by sewage, or if systems have been inspected or repaired
  • Where a system has not been in regular use nor regularly flushed

What should be done?
Fernox offers a silver catalysed hydrogen peroxide treatment, Fernox LP Sterox.

Fernox LP Sterox
This product treats a wide spectrum of biocidal activity including all water-borne bacteria and viruses. It is particularly valuable in modern water system hygiene management where more conventional treatments such as chlorination are unsuitable. Fernox LP Sterox is supplied in one litre bottles. This will treat 300 litres of system water. After treatment, it is not critical that Fernox LP Sterox is flushed from the water supply as it naturally decomposes to water and oxygen.

Water should be run from each outlet and tested with a Fernox LP Sterox Test Strip until the concentration in the water is less than 200ppm.

Power Cleaner is phosphate, nitrate and nitrate-free and is developed to exceed all regulatory and legislative guidelines in regard to the environment impact of the formulation. It is compatible for use in mixed metal heating systems, including aluminium.

Power Cleaner F8 can be dosed into the system up to a week before flushing. This high performance, strong cleaner is effective after one hour circulating under normal operating conditions.

Power Cleaner F8 is a pH neutral cleaner which has low environmental impact and can be safely disposed via foul drain.

You will get a very good system clean with both products. However, if the system is especially dirty it is recommended to use the stronger Power Cleaner F8 which will have an increased dispersion effect, even at low temperatures.

No. Whilst Power Cleaner F8 is formulated with citric acid, this is neutralised in-situ to form the neutral citrate species which has such an effective cleaning action.

Citrate action is a term used to describe the powerful chelating effect that the citrate ion has on metal ions. This strong binding effect means that corrosion debris is lifted and transported out of the system during a system clean.

Power Cleaner F8 is pH neutral and is not acidic, therefore no neutralisation is needed. This saves time on-site.

Power Cleaner F8 is a concentrated formulation supplied in 500ml bottles, to reduce packaging waste. Just one bottle treats larger systems of 130 litres, 16 radiators or 250 sqm of underfloor systems and one dose is sufficient for cleaning the central heating systems of up to 97% of all UK homes (or larger heating systems).

Make sure the system is turned off and allow radiators to cool down (1). Select a radiator and shut both the wheel-head and lock shield valves (2). If a thermostatic radiator valve (TRV) is fitted, close it by turning it to the minimum setting.

Having removed the air vent pin using a cloth to absorb any escaping water (3). Screw the Fernox Express injection nozzle into the air vent (after cutting to the right diameter to fit tightly (4)). Fit the tube to the adapter and screw onto the canister. Attach the other end of the tube onto the nozzle in the radiator (5).

Re-open the wheel-head valve (6) (or TRV) and inject all the content of the Fernox Express by squeezing the trigger for 30 seconds (7). After the product has been dispensed close the wheel-head valve (8) (or TRV), remove the injector nozzle and tighten the air vent pin (9). Open both radiator valves, turn on the central heating system (10) and let it run for 15 minutes to allow the Express to disperse around the system.

Fernox Express can also be for dosed via the system filling loop using the appropriate special adapter supplied with the Express product as well as via the bleed valve on a fitted Fernox TF1 Filter. The whole process takes less than two minutes.

This is an innovative, universal inhibitor package which uses the proven inhibition qualities of Fernox Protector F1 with an active dispersant.

This unique formulation is designed to detect, lift and deliver magnetic and non- magnetic debris to an in- line system filter.

No, the TF1 Omega Filter has been designed to ensure that even when it reaches a level of maximum collection, system water can still pass through the filter, short-circuiting the body, and flowing freely through the manifold.

The TF1 Omega Filter is a high performance, nickel plated, in-line system filter, which is designed for domestic heating systems.

It is produced with quality materials and components and has been manufactured using precision engineering. Combining the strength of a powerful Neodymium magnet with Hydronic Particle Separation technology, the TF1 Omega Filter offers a superior collection capacity for both magnetic and non-magnetic debris.

The TF1 Omega Filter out performs other filters of its size by collecting significant quantities of system contaminants, and competes with many larger filters thanks to the cleverly designed internal mechanisms of the filter.

The HPS technology improves the overall collection of the filter, as well as the performance of the Neodymium magnet.

How do Fernox Cleaners work?
The Fernox Express Inhibitor Test Walkthrough Demo
The New Fernox Express Inhibitor Test
Fernox – Why Use Water Treatment
The Power of Fernox F1 Protector – Time Lapse
How to dose with Fernox Express via a radiator
TF1 Sigma – Precision Engineered Filter
How does Fernox Anti-freeze work?
How does Fernox Biocide F7 work?
How do Fernox Scale Reducers work?
How to use a Fernox Powerflushing Machine
The TF1 Omega Filter
How do you install a Fernox TF1 Omega Filter?
How do you clean a Fernox TF1 Omega Filter?
How does a Fernox TF1 Omega Filter Work?
Stop Boiler Breakdown with Powerflushing
The Fernox TF1 Total Filter
How to Install Fernox TF1 Compact
How to dose with Fernox Express via TF1 Omega Filter
How to clean a TF1 Omega Filter – in less than a minute!
Fernox TF1 Omega Plus – Next Generation, High-performance Filter
Fernox – How To Use Our Universal Test Kit
The Fernox Express Range
How does Fernox Protector F1 work?
How does Fernox Filter Fluid+ Protector Inhibitor work?
How does Fernox Boiler Noise Silencer F2 Work?
How does Fernox Leak Sealer F4 work?
How to use System Water Test
How to use Water Quality Test
How to use the Protector Test Kit
How does Fernox Cleaner F3 work?
How to dose via a radiator
Fernox TF1 Sigma HP Filter – designed to protect Air and Ground Source Heat Pumps
Simple steps to dose Fernox Express via a radiator
How does Fernox Protector+ Filter Fluid F9 work


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