Glow-worm Hideaway Boiler Guide (All Models: 40–120 Series)

The Glow-worm Hideaway range was built to last, but most boilers in this family are now between twenty and forty years old. Even with regular servicing, parts wear out, seals weaken, and efficiency declines. The issues below are the most common across the Hideaway 40–120 series, along with what typically causes them, how engineers diagnose them, and what homeowners can realistically expect in terms of repair or replacement.

Boiler not firing up
This fault appears most often in the later 100CFF and 115CFF models, which use fan-assisted flues and ignition PCBs. You may hear the fan start up, but the burner doesn’t light. Common causes include a failed ignition PCB, faulty gas valve, or low gas pressure. Sometimes the air pressure switch fails to signal that the fan is running, preventing ignition entirely. Resetting the boiler may restore operation temporarily, but if it keeps happening, it usually points to internal component wear. Engineers can test for voltage on the ignition board and gas valve, but because original PCBs are discontinued, repairs depend on finding refurbished parts. Replacements often cost £250–£400 and aren’t always reliable.

Pilot light keeps going out (B & BF models)
Older 40B, 50BF, and 70BF models rely on a permanent pilot flame that should stay lit. If it keeps going out, the thermocouple may be faulty or the pilot jet blocked with dust or soot. The thermocouple acts as a safety sensor, shutting off gas flow if no flame is detected. Over time, heat exposure causes it to fail. Cleaning the jet can help, but once parts start to degrade, relighting becomes a daily routine for some homeowners. Because most pilot assemblies and thermocouples are no longer made, even simple faults like this can signal the boiler’s end of life.

Kettling or loud rumbling noises
A loud, boiling sound during operation is caused by limescale or sludge buildup inside the heat exchanger. This is particularly common in the 60B and 70B series, which often ran for years without water treatment. The deposits restrict water flow, creating hot spots that cause water to boil locally. An engineer can carry out a chemical flush or add a descaling treatment, but these are temporary solutions. Once the internal waterways are scaled up, efficiency drops sharply, and overheating becomes more frequent. In many cases, replacement is more cost-effective than repeated cleaning.

Overheating and tripping
If your Hideaway cuts out after running for only a few minutes, it’s likely overheating. The main reasons are sludge buildup in pipework, poor circulation, or a faulty thermostat. You may notice the boiler clicking on and off frequently as it tries to regulate temperature. Older models like the 80BF and 100B rely on mechanical thermostats that eventually lose calibration. Replacing these is sometimes possible, but with parts now scarce, long-term reliability remains poor. Repeated overheating can also damage the PCB or trip the high-limit thermostat.

No heating or hot water
When both heating and hot water stop working, it often points to a failed pump or blocked heat exchanger. In systems with separate controls, a stuck diverter valve can also cause the issue. Hideaway boilers like the 50FF or 70CFF use traditional mechanical pumps that can seize after decades of use. An engineer might try to free the pump manually, but even if it runs again, it often seizes soon after. Corrosion inside the system and sludge contamination make this one of the most expensive recurring faults in older boilers.

Fan failure (FF/CFF models)
Fan-assisted models such as the 60CFF, 80FF, and 100CFF rely on a small motorised fan to move exhaust gases safely through the flue. Over the years, fan bearings dry out or seize completely. You might hear a humming noise when the boiler starts, but no ignition follows. Fan replacements, when available, cost around £250–£350 with labour, though sourcing genuine Glow-worm fans has become extremely difficult. In some cases, engineers fit reconditioned units, but results vary. Fan failure is one of the clearest signs that the boiler is nearing the end of its usable life.

Flue or ventilation blockage
Early open-flued and balanced flue models depend on clear airflow around the casing. Dust, spider webs, and even nesting debris can partially block the flue, reducing combustion efficiency. Homeowners might notice yellow flames or staining around the boiler casing. This is especially risky in open-flued versions such as the 40L and 50B, as incomplete combustion can release carbon monoxide. An engineer will check the flue for blockages and test combustion levels, but most recommend upgrading to a sealed system for safety and efficiency reasons.

Leaks or corrosion
Corrosion is inevitable in systems that have been operating for decades. Small drips under the boiler, rust on the pump housing, or damp patches near pipe joints are all warning signs. The Hideaway 90BF and 120B models in particular suffer from internal leaks due to aging heat exchangers and perished seals. Once the metal begins to rust through, sealing or patching rarely holds. Even minor leaks can damage electrical parts and cause intermittent cutouts. In most cases, engineers will advise replacing the boiler entirely.

Low pressure or cold radiators
A system that regularly loses pressure or has cold spots in radiators usually has airlocks or slow leaks. You can repressurise the system or bleed radiators, but recurring pressure drops often point to corrosion in pipework or a failing expansion vessel. In older Hideaway installations, expansion vessels were external and often forgotten during servicing. Replacing them can help temporarily, but if pressure loss continues, there’s likely a hidden leak that’s not worth chasing in a 30-year-old system.

Soot or black marks near the flue
If you see soot or scorch marks around the flue or on the boiler casing, it’s a sign of incomplete combustion. This can mean a blocked burner, poor ventilation, or failing seals inside the combustion chamber. It also indicates potential carbon monoxide risk. This issue appears frequently in open-flued Hideaway models, especially the 40L and 50L, where airflow depends on room ventilation. The safest course of action is to turn the boiler off and contact a Gas Safe engineer immediately.

Boiler cycling on and off
Some Hideaway boilers repeatedly switch on for a few seconds, then shut off again without heating the water properly. This is known as short cycling. It usually happens when the thermostat or flow sensor fails, or when water can’t circulate properly due to sludge. Cycling not only wastes gas but also increases wear on the fan and ignition components. In the 100FF and 115CFF, these faults often occur alongside overheating or ignition problems.

Parts discontinued
This is the biggest limitation facing any Glow-worm Hideaway owner today. Glow-worm stopped manufacturing Hideaway components over a decade ago. That means key parts like PCBs, thermocouples, fans, and thermostats are no longer available new. Engineers sometimes rely on reconditioned parts from older stock, but availability changes constantly and there’s no warranty on many of them. Even if a repair is possible, it often buys only a few extra months of operation before something else fails. At this stage, replacement is almost always the more sensible investment.

Summary
Most Glow-worm Hideaway boilers have outlasted their expected lifespan several times over. While they were well-built, age and efficiency standards have overtaken them. Many issues — from ignition faults to leaks and corrosion — are repairable once or twice, but continued breakdowns quickly outweigh the cost of replacement. Because all Hideaway models are non-condensing and depend on discontinued parts, upgrading under the ECO4 scheme is the most practical long-term solution. It eliminates ongoing repair bills, improves efficiency, and provides a safer, modern heating system with full warranty coverage.