Glow-worm Space Saver RF & RFS Boiler Guide

The Glow-worm Space Saver RF and RFS ranges were built to offer compact, room-sealed heating options for homes during the late 1980s and early 1990s. While reliable for their time, these boilers are now well past their intended lifespan. The RF models use a standard room-sealed flue, while the RFS versions incorporate a fan-assisted system for improved combustion control. Although this was advanced for its era, ageing electrical and mechanical components have made these units increasingly unreliable today.

Fan failure (RFS models)

Fan faults are the most common issue with the Space Saver RFS models, particularly the RFS 40, 50, and 60. Over time, fan bearings seize or the motor windings weaken, preventing proper airflow through the flue. When the fan speed drops, the proving switch fails to detect sufficient airflow, stopping ignition altogether. Even if the fan operates intermittently, it can cause the boiler to short cycle or lock out. Replacement fans are now rare, and refurbished parts tend to fail again within months.

Ignition and flame failure (RF and RFS models)

Both RF and RFS units can suffer from ignition failure, often caused by worn spark electrodes or damaged ignition leads. The insulation surrounding the electrode can degrade over time, producing a weak spark that cannot reliably ignite the gas. On fan-assisted RFS boilers, ignition also depends on correct fan speed, so slow or intermittent fans can cause ignition lockouts. Ageing control boards further compound the issue, leading to inconsistent lighting or early flame dropout.

Pilot light or flame instability (RF models)

The non-fan RF models sometimes develop unstable flames or frequent pilot outages. This typically happens when dust or corrosion affects the burner or when the gas valve struggles to maintain steady pressure at low flow rates. The result is a pilot flame that flickers or goes out after heating up. Thermocouple wear is also common on these models, and replacement parts are now discontinued.

Overheating and shutdowns (RF and RFS 60 models)

Higher-output versions like the RF 60 and RFS 60 are prone to overheating when circulation slows due to sludge or scale buildup. The overheat thermostat cuts power to prevent damage, but repeated shutdowns indicate underlying flow restrictions. A worn pump or scaled heat exchanger usually causes this problem. Continued overheating can crack internal seals or lead to heat exchanger leaks.

Kettling and boiling noises (All models)

A loud rumbling or boiling sound during operation indicates severe scale buildup inside the heat exchanger. This is a common problem for all RF and RFS units, especially those installed in hard water regions. As limescale accumulates, it traps hot spots and causes localised boiling. The result is the characteristic kettling noise and reduced efficiency. Chemical flushing can quieten the noise temporarily, but corrosion usually returns soon after.

Leaks and corrosion (RFS 50 and 60 models)

Fan-assisted boilers operate at slightly higher internal pressures, making them more susceptible to leaks as joints age. Corrosion around the pump housing, pipe connections, and expansion vessel is frequent on the RFS 50 and 60. Once the main heat exchanger or internal manifold begins leaking, repair is no longer cost-effective. Water ingress can also damage nearby electrical components, leading to repeated ignition and fan faults.

Thermostat and control faults (RF and RFS 60 models)

Mechanical thermostats degrade with time, becoming inaccurate or sticking in one position. Faulty thermostats cause erratic temperature control and short cycling, which increases wear on other components. Replacement thermostats for both RF and RFS versions are now obsolete, and fitting modern equivalents requires complex electrical modifications.

Pressure and circulation problems (RF 50, RFS 50, and RFS 60)

Poor circulation leads to slow radiator heating and intermittent boiler operation. In many cases, internal sludge or debris from corroded radiators restricts water flow through the system. The result is noisy operation and uneven temperatures around the home. The problem is particularly common in the 50 and 60 kBtu models, which used smaller circulation pumps that weaken over time.

Flue blockages and proving switch issues (RFS models)

The RFS models rely on a fan-proving switch to confirm that the flue is clear before ignition. When deposits form in the flue or the proving switch fails, the boiler cannot light. These switches are delicate and prone to sticking with age. A partially blocked flue or faulty pressure tubing can trigger repeated ignition lockouts. Regular cleaning may help temporarily, but replacement parts are scarce and unreliable.

General age-related decline (All models)

After more than three decades of use, internal corrosion, electrical degradation, and part wear are unavoidable. Components such as the gas valve, fan, and control board are now obsolete. While minor repairs can restore operation briefly, repeated faults are typical as the boiler continues to deteriorate. In most cases, upgrading to a modern A-rated boiler is more reliable and economical than continuing repairs.

While some RF and RFS boilers can still be repaired, the combination of discontinued parts and recurring mechanical faults makes long-term maintenance uneconomical. Replacing the unit with a modern condensing boiler offers immediate improvements in efficiency, safety, and reliability.