Can you fix a unit that's locking out?

Almost always, yes. Common causes are flame supervision, gas valve, fan motor or pressure switch faults. We diagnose on the first visit and quote the fix before doing it.

My heat exchanger is cracked, can it be repaired?

No, a cracked heat exchanger is the end of life for any warm air unit, the airstream the unit is blowing at occupants is the same airstream that's in contact with the exchanger. We'll quote a replacement, like-for-like or upgrade.

Should I replace warm air with radiators?

Sometimes, depending on house layout, ductwork condition and your tolerance for disruption. We'll give an honest view, sometimes a modern condensing warm air unit is the better answer, sometimes a wet system upgrade is. Quoted both ways.

Do you do commercial Powrmatic / Benson / Reznor?

Yes, commercial direct-fired and indirect-fired warm air heaters, single units or banks, service contracts and replacements.

Do you check the ductwork too?

Yes, filters, return air path, grille airflow and duct condition. The most-skipped part of warm air servicing, and often the source of 'unit not heating properly' complaints.

Warm Air · Ducted Heating · Gas Safe

Warm Air Heater Service,
Repair & Replacement

Genuine specialist cover for ducted warm air systems, Johnson & Starley, Powrmatic, Benson and Reznor, with full service, repair, ductwork checks and like-for-like or modernised replacement when the unit is past it.

Book warm air engineer 07584 076105 07702 523464

J&S · Powrmatic · Benson · Reznor · Gas Safe specialist

Johnson & Starley trained
Commercial & domestic warm air
Ductwork inspection included
Honest repair-vs-replace advice
Genuine OEM parts where available

Service overview

What warm air heater service, repair & install actually involves.

Plain-English breakdown, so you know exactly what you're paying for, and why it matters before we set foot on site.

What it is

Service, repair, fault diagnosis and replacement of gas-fired warm air heaters, domestic ducted units (Johnson & Starley Hi-Spec, Aquair, WarmCair) and commercial direct/indirect fired heaters (Powrmatic, Benson, Reznor, Ambirad), including ductwork and grille checks.

Who it's for

Owners of 1960s–1990s homes with original ducted warm air heating, light industrial and warehouse occupiers, churches and village halls with overhead warm air units, and facilities managers maintaining commercial heater banks.

When you need it

Annual service overdue, recurring lockouts, loss of flame, sooting or carbon monoxide concerns, weak airflow at grilles, noisy fans, slow warm-up, or a quote for like-for-like replacement when the unit is past economic repair.

Why it matters

Warm air heating is increasingly a specialist field, most domestic engineers haven't worked on a J&S Hi-Spec and most commercial gas engineers don't routinely touch ducted units. A specialist visit catches sooting, cracked heat exchangers and dangerous combustion drift early, and an honest repair-vs-replace conversation saves owners from sinking money into a unit at end of life.

The cost of doing nothing

What goes wrong when this is ignored.

Warm air units fail in ways that domestic boiler engineers don't always recognise, and the consequences can be quietly serious before they become obvious.

Risks of waiting

Cracked heat exchangers leak combustion gases into the airstream, the only system in your home that's designed to blow that air at you.
Sooting at the burner is a sign of incomplete combustion and a CO red flag, easily missed without a proper combustion analysis.
Failed flame supervision devices can let unburnt gas accumulate in the burner chamber, then ignite.
Blocked or collapsed ductwork chokes airflow and overheats the heat exchanger from the inside.

Common mistakes

Letting a domestic boiler engineer 'have a look' at a J&S Hi-Spec, the fault patterns and parts catalogue are different worlds.
Skipping annual servicing because 'it still warms up', warm air units degrade silently between failures.
Patching up a unit at 30+ years old when a modern replacement would pay back in 4–5 winters.
Forgetting the ductwork, dirty filters, blocked grilles and disconnected runs make any warm air install perform poorly.

Our process

How the job actually runs.

Same system every time. No improvising on your floor.

01

On-site diagnosis

We listen to symptoms, check fault history if available, inspect the unit, ductwork, return air path, grilles and any flue components.
02

Combustion analysis

Calibrated flue gas analyser reading at the burner, gas pressure check at the inlet, flame supervision test, heat exchanger inspection where accessible.
03

Repair or replace recommendation

If the fault is repairable on an economically viable unit, fixed-price repair quote. If the unit is end-of-life, an honest replace quote with options.
04

Carry out the work

Parts sourced from OEM or specialist refurb stockists. Replacements with like-for-like J&S Aquair / WarmCair, or upgrade to a modern condensing wet-system alternative.
05

Commission & paperwork

Combustion readings recorded, ductwork airflow tested at representative grilles, service report or commissioning certificate issued.

What you get

The outcomes that matter.

Genuine warm air specialism

Most engineers don't work on ducted units regularly, we do. Trained on Johnson & Starley, Powrmatic and the commercial direct/indirect fired range.

Honest repair-vs-replace advice

If a 30-year-old unit is at end of life, we'll say so. If the fault is a £180 fix on a unit with another decade in it, we'll do the fix.

Ductwork looked at, not ignored

Filters, grilles, return paths and run condition all checked, the part most engineers skip.

Safety-first combustion checks

Combustion analysis on every service, flame supervision tested, heat exchanger inspected. CO risk taken seriously.

Genuine parts where possible

OEM J&S, Powrmatic and Reznor parts via authorised stockists, refurb/specialist sources where OEM is discontinued.

Domestic and commercial

Same engineer covers a J&S Hi-Spec in a Hertfordshire family home and a Powrmatic bank in a warehouse.

In depth

Everything worth knowing before you book.

The details a salesperson skips. Skim it, or read every word, both are useful.

Questions on this?

Talk to a Gas Safe engineer direct.

07584 076105 07702 523464

Why warm air is increasingly specialist

Ducted warm air heating was common in UK homes built in the 1960s–1980s, then largely displaced by wet radiator systems. Many of those original units (Johnson & Starley Hi-Spec, Aquair and the later WarmCair range) are still running, but the engineers who know them are retiring. We've kept the specialism alive because warm air, when properly maintained, is a fast, responsive and surprisingly efficient way to heat a home.

Common Johnson & Starley faults

Failed fan motors, sticking gas valves on early Hi-Spec units, cracked heat exchangers (the unit-ending fault), failed flame supervision devices, blocked condensate drains on the modern WarmCair condensing range, and air filter neglect choking the return air path. Most are repairable on a unit under 20 years old, the heat exchanger crack is usually the end of the line.

Commercial direct-fired vs indirect-fired

Direct-fired commercial warm air heaters (Powrmatic NV/NVx, Benson) inject combustion products directly into the heated airstream, suitable only for well-ventilated industrial spaces with no occupancy proximity concerns. Indirect-fired units (Reznor, Powrmatic CPx) use a sealed heat exchanger and a separate flue, suitable for occupied workshops, warehouses and retail. We work on both, with the correct testing procedures for each.

Repair vs replace, the honest call

A Johnson & Starley unit from the 1990s with a healthy heat exchanger and a £180 fan fault is worth fixing. The same unit with a cracked heat exchanger isn't, the part alone (where still available) is £600–£900 plus a day's labour, on a 25+ year old chassis. A modern J&S WarmCair condensing replacement, or a conversion to a wet radiator system with a high-efficiency boiler, usually pays back inside 5 winters on gas savings alone.

Ductwork is half the system

Even a perfectly serviced unit can't push warm air through choked ductwork. We pull and clean return air filters (often unchanged for years), check the duct runs for collapsed insulation and disconnected joints, and verify airflow at representative grilles. On older installs, a duct clean and rebalance often delivers more felt improvement than the heater service itself.

General work gallery