Radiant tube heaters are the long steel tubes with polished reflectors hung above warehouse racking, workshop floors and sports halls. They heat people, floors and stock directly rather than the air, which suits big, draughty buildings where the loading doors are open half the day.
Being high up and out of sight is also their weakness. Reflectors gather dust, burners clog, fans wear, tubes sag, and stock creeps closer than the manufacturer allows. Often the first anyone hears of it is a heater locking out on a cold November morning.
This guide covers how radiant tube and plaque heaters work, what a proper service includes according to the manufacturers' own instructions, the common faults, and when to replace rather than repair. If your site also runs warm air heaters, see our separate guide to warm air heater servicing.
The short answer
- Radiant tube and plaque heaters are gas appliances. Employers must keep them safe, and manufacturers specify an annual service, more often in dusty buildings.
- A proper service follows the manual for that model: burner, injector and electrodes, fan and air pressure switch, gas pressures, tubes, turbulators, reflectors, flue, hangers, clearances, controls and a written record.
- Unflued heaters, including most plaque heaters, release combustion products into the building, so the ventilation must be checked at every service.
- Repeated lockouts usually mean dirty or cracked electrodes, an air pressure switch that won't prove, a blockage or a gas pressure problem. Reset once, then call an engineer.
- New radiant heaters must meet Ecodesign efficiency and NOx limits, so a replacement may not be a straight swap.
- The engineer should hold CORT1, the commercial qualification for overhead radiant tube and plaque heaters. Stephen holds it.
How radiant tube heaters work
A burner at one end of a steel tube fires hot combustion gases along it. The tube gets hot enough to give off infrared heat, and a reflector above it throws that heat down to the floor. When a loading door opens the warm air escapes, but the heat already absorbed by the floor, racking and people does not. The main parts are:
- Burner unit: gas valve, injector, burner head, ignition and flame-sensing electrodes and a control board, in a box at one end.
- Combustion fan and air pressure switch: the fan pushes air into the burner or, more often, draws the gases along the tube. The pressure (vacuum) switch proves the fan is working before the gas valve can open.
- Emitter tube and turbulators: the first length after the burner runs hottest. Twisted turbulators in later sections slow the gases so the far end still gives useful heat.
- Reflector: the polished canopy that directs heat downwards. A dusty reflector means less heat for the same gas.
- Flue: on flued heaters, the pipe that takes combustion products outside.
Linear heaters run straight, with the burner at one end and the exhaust at the other, and suit long aisles. U-tube heaters double back through a return bend, so the hot first leg sits beside the cooler return leg and the heat is more even, which suits zone and spot heating. Both must hang at the slope the manufacturer specifies.
Most sites have single-burner heaters, each self-contained. Larger buildings may have a continuous (multi-burner) system, where several burners fire in series along a network of tubes and one exhaust fan keeps the whole system under suction. If that fan, its damper or its condensate trap has a problem, a whole branch can go off at once.
Flued (Type B) heaters discharge combustion products outside. Unflued (Type A) heaters release them into the building, which is only acceptable with designed ventilation. Luminous plaque heaters burn gas across a ceramic plaque that glows red. They run much hotter than tubes, are mounted higher, and are usually unflued. A cracked plaque burns badly and can let the flame light back towards the injector.
Choosing a heating system for a new or refitted building is a separate decision. This guide is about keeping existing radiant heaters safe and working.
What a proper radiant heater service covers
Regulation 35 of the Gas Safety (Installation and Use) Regulations 1998 requires employers to keep workplace gas appliances, flues and pipework in a safe condition. The regulation doesn't set a frequency, but the manufacturers do. AmbiRad/Reznor's radiant heater manuals call for an annual service by a competent person, and more often in dusty or polluted conditions. Factories and agricultural premises are technically outside those regulations, but the general duties under the Health and Safety at Work etc. Act 1974 still apply, so the standard in practice is the same.
A good service follows the instructions for that make and model. Drawing on current AmbiRad/Reznor and Space-Ray manuals, it should include:
- Burner removed and cleaned. The injector is checked and replaced if contaminated or blocked. Some current AmbiRad/Reznor models call for a new igniter at every service.
- Electrodes cleaned, ceramics checked for cracks, spark gap set, and connections made secure. Flame-sense current is measured where the manufacturer gives a minimum.
- Combustion fan: impeller and housing cleaned, the impeller checked to spin freely, bearings checked for wear.
- Air pressure switch: sensing tubes checked for splits, blockages and condensate, and the switch proved to operate.
- Gas pressures and heat input checked against the data plate, with a combustion check where the manufacturer specifies one.
- Tubes: brushed down, checked for sag, holes, scaling and heavy discolouration, and joints checked. Where the manual says to, the turbulators are withdrawn, cleaned and refitted in the right number and position.
- Reflectors cleaned and checked for corrosion. AmbiRad notes this can noticeably improve the heat delivered.
- Flue, air inlet and condensate drains checked for obstruction, sound joints and supports.
- Hangers: chains, drop rods and fixings checked for wear and corrosion, with room for the tubes to expand. Flexible gas connections checked and replaced at the manufacturer's interval.
- Clearances and controls checked (see below).
- Ventilation checked, including CO2 readings for unflued heaters.
- Safe operation: light-up, flame failure and shutdown, plus a tightness test of the installation pipework.
- Written record for each heater, with location, model, readings, defects and recommendations.
Clearances: the check that gets missed
Every manufacturer publishes minimum clearances to combustible materials. For common U-tube models that is roughly 1.5 to 2.5 metres below the tubes, depending on output, plus smaller distances to the sides and above. Racking gets moved and stock gets stacked higher, and the clearance quietly disappears. Space-Ray asks installers to post the maximum stacking height near the heaters, which is good practice anywhere. Keep sprinkler heads, light fittings, cabling and plastic rooflights out of the clearance zone too.
Controls
Many radiant systems use a black bulb sensor rather than an air thermostat, because it responds to radiant heat and reads closer to what people actually feel. If new racking has shaded it or it has been moved, the heaters will over- or under-heat.
Unflued heaters and plaque heaters
BS 6896 covers the installation and maintenance of gas-fired overhead radiant heaters, and BS EN 13410 sets ventilation requirements for non-domestic premises. Manufacturers' manuals based on it limit CO2 to 0.28% where people breathe, and size mechanical extract at no less than 10 cubic metres per hour per kW of heat input, interlocked with the heaters. At each service the engineer checks that vents haven't been blocked or closed and that interlocks work, then takes CO2 readings once the heating has run at full load. A new mezzanine or sealed roof vents can undo the original design.
On plaque heaters the plaque is removed carefully, cleaned, checked for cracks and replaced if damaged. Once relit it should glow evenly, and dark patches point to damage. On continuous systems the exhaust fan, damper, couplers and condensate trap get their own checks. AmbiRad rules out copper condensate drains and calls for external runs to be frost-protected, which matters through a Scottish winter.
Common faults and what usually causes them
Most faults show up as a lockout: the heater fails to light or loses its flame and shuts down for safety. Finding the cause is a job for a Gas Safe engineer qualified for radiant heaters.
- No spark, not lighting. Usual causes: Dirty or cracked ignition electrode, wrong spark gap, failed lead or control board, or no call for heat.
- Lights, then locks out. Usual causes: Dirty or cracked flame-sensing electrode, a poor earth or reversed polarity, low gas pressure, or a partly blocked injector.
- Fan runs, burner never tries. Usual causes: Air pressure switch not proving: split or blocked sensing tube, condensate, dirty fan, blocked flue or inlet, leaking tube joint, or a failed switch.
- Fan won't start. Usual causes: Failed motor or seized bearings, wiring fault, or pressure switch stuck.
- Tube discoloured or sagging. Usual causes: Over-firing, missing or misplaced turbulators, supports too far apart, or a tube binding so it can't expand. Some darkening of the first length is normal.
- Water from the exhaust. Usual causes: Condensation in a long or cold flue, a blocked or frozen drain, or a flue not falling to the terminal.
- Noise. Usual causes: Worn fan bearings or dirty impeller. Ticking as tubes heat and cool is normal, but banging usually means a tube binding on a hanger.
Resetting a lockout: one reset is reasonable. If it locks out again, leave it off and call an engineer. AmbiRad tells users to isolate the heater after three lockouts in a row. Repeated resetting can hide a fault that matters.
Working at height: planning the service
Radiant heaters are usually mounted at least three or four metres up and often much higher, so every service is work at height. The Work at Height Regulations 2005 apply in Scotland and require the work to be planned, using equipment that prevents falls. On most sites that means a scissor lift or other MEWP, not ladders. AmbiRad's manuals warn against resting ladders or anything else on the heaters.
- Book in late summer. Heating is often needed in the west of Scotland from September, and parts for older heaters can take time.
- Agree access in advance: which aisles can close and when, forklift routes, loading times, and floor protection for sports halls.
- Phase the work so part of the building stays heated.
- One date, one record. Put radiant heaters on the same schedule as your boilers and other gas plant, ideally under a planned maintenance contract.
Repair or replace?
Most faults are repairs: electrodes, igniters, injectors, fans, pressure switches, control boards, gas valves, and sometimes a tube section or reflector. Replacement starts to make sense when burners or controls are obsolete and parts can't be sourced, when the tube is holed, split or badly sagged on an otherwise old heater, when the same unit keeps failing, or when racking and mezzanines have left heaters in the wrong place. Any new electrical supply or control wiring is carried out through our approved, separately registered contractor.
Ecodesign rules for new heaters
Since 1 January 2018, new gas tube heaters and luminous heaters sold in Great Britain have had to meet Regulation (EU) 2015/1188, which still applies here as assimilated law. For commercial heaters up to 120 kW, the minimum seasonal efficiency is 74% for tube heaters and 85% for luminous heaters, and NOx is capped at 200 mg/kWh of input.
The EU tightened these from 1 July 2025 to 80%, 90% and 180 mg/kWh. The UK Government consulted in spring 2026 on matching them, and its own assessment estimated around two-thirds of tube heater products on sale would be removed from the market. None of this forces a safe, working heater out. But a modern replacement may have a different burner, output or flue arrangement, so it needs specifying rather than assuming a like-for-like swap.
Heaters that are removed must have their gas supply properly disconnected and capped by a Gas Safe registered engineer. Our guide to capping off and decommissioning explains what that involves.
Who should service radiant heaters?
Gas Safe registration alone isn't enough. Overhead radiant heaters have their own commercial assessment, CORT1, which covers luminous plaque heaters and both flued and unflued radiant tube heaters. It sits on top of a commercial core gas qualification and is renewed every five years. Stephen holds CORT1, along with the commercial qualifications for warm air heaters (CIGA1 and CDGA1) and commercial pipework (ICPN1, TPCP1 and TPCP1A).
Whoever you use, ask to see their Gas Safe ID card. The back lists the gas work they are currently qualified for, and you can check the licence number on the Gas Safe Register website.
Carbon monoxide: warning signs
A badly burning heater, or an unflued heater in a building with compromised ventilation, can produce carbon monoxide, which you can't see or smell. Watch for staff with headaches, dizziness, nausea or tiredness that ease outside, a stuffy atmosphere when the heaters run, soot around a burner or flue, or a plaque glowing unevenly.
If you suspect carbon monoxide: switch the heaters off if it is safe to, open doors, get people into fresh air and keep the heaters off until they have been checked. Call the National Gas Emergency Service on 0800 111 999. Anyone with symptoms should get medical advice, and call 999 if someone is struggling to breathe or has collapsed.
How Titan Heat can help
Titan Heat services and repairs natural gas radiant tube heaters, continuous systems and plaque heaters in warehouses, factories, workshops, vehicle workshops and garages, sports halls, agricultural buildings and churches across Glasgow, Lanarkshire and Central Scotland. We are Gas Safe registered (business registration 982732), and Stephen holds CORT1. We offer annual servicing to the manufacturer's instructions with a record for every heater, fault-finding and repair, ventilation checks on unflued installations, decommissioning, and radiant heaters as part of a planned maintenance contract alongside your other gas plant.
See our commercial heating services and our page for warehouses and distribution centres. To arrange a service or report a fault, use our commercial enquiry form. Tell us how many heaters you have, the make if you know it, roughly how high they are and any symptoms.
Frequently asked questions
How often should a radiant tube heater be serviced?
At least once a year, as the manufacturers specify, and more often in dusty buildings. Late summer is best, so parts can be ordered before the heating season.
Why does my radiant heater keep locking out?
Usually dirty or cracked electrodes, a poor earth, an air pressure switch that won't prove, a blocked flue or fan, or low gas pressure. Reset it once. If it locks out again, leave it off and call a Gas Safe engineer qualified for radiant heaters.
Do radiant heaters need a gas safety certificate?
There is no named certificate as there is for rented homes, but employers must keep workplace gas appliances safe. An annual service gives you a written record for each heater, which insurers and landlords often ask to see.
What does a plaque heater service involve?
The ceramic plaque is removed, cleaned gently, checked for cracks and replaced if damaged. The injector and reflector canopy are cleaned, and because most plaque heaters are unflued, the ventilation is checked with CO2 readings.
Do unflued radiant heaters need extra ventilation?
Yes. The ventilation has to be designed for them in line with BS EN 13410, and checked at every service and after any building alterations.
Can an old radiant heater be replaced like for like?
Not always. New heaters must meet Ecodesign efficiency and NOx limits, and many older models are discontinued, so a replacement should be specified for the space.
