Glow-worm Space Saver B & F Boiler Guide

The Glow-worm Space Saver B and F range was a durable line of boilers for its time, but most units are now well beyond their expected service life. These boilers were compact and efficient when introduced, yet age, corrosion, and component fatigue now cause recurring issues. The “B” models feature balanced flues, while the “F” models use fan-assisted flues. Although both types share many components, the fan-assisted variants have additional electrical and mechanical failure points due to the added fan assembly.

Fan failure (Space Saver F models)

Fan-assisted models such as the Space Saver 50F, 60F, and 70F often develop fan faults after years of use. Bearings dry out or seize, and the motor windings weaken due to heat exposure. When the fan slows or fails, the boiler cannot vent combustion gases effectively, which causes ignition lockouts or safety shutdowns. Replacement fans for these older models are now difficult to source, and refurbished parts have a short lifespan.

Pilot light keeps going out (Space Saver B models)

The open-flued Space Saver B models frequently suffer from pilot lights that will not stay lit. This is typically due to a weak thermocouple or a blocked pilot jet restricting gas flow. Sometimes, draughts entering through the balanced flue can disturb the flame. Cleaning the pilot assembly or fitting a new thermocouple may restore normal operation, but persistent failure often indicates the gas valve is wearing out internally.

Ignition or flame failure (Space Saver F models)

On the fan-assisted “F” models, ignition problems are a common symptom of worn spark electrodes or faulty fan-proving switches. The ignition sequence depends on the fan running at full speed, so if the proving switch fails to detect airflow, the boiler will not light. Electrical degradation and moisture corrosion in the wiring loom are also common after decades of service. Once these issues start, they usually return even after repair.

Overheating and frequent lockouts (Space Saver 60B, 70B, 60F, 70F)

The larger-capacity models, both B and F variants, are more prone to overheating due to scale and sludge accumulation in the heat exchanger. Restricted water flow prevents proper heat dissipation, triggering safety cut-outs. A failing circulation pump or a sticky thermostat can worsen the issue. Overheating also stresses the exchanger joints, increasing the risk of leaks and internal corrosion.

Kettling noises and limescale buildup (All models)

A loud rumbling or boiling noise during operation is caused by limescale deposits forming inside the heat exchanger. This affects all Space Saver B and F units, especially those in hard water areas. Scale traps heat locally, causing small steam bubbles that produce the familiar “kettling” sound. A chemical flush can quieten the system temporarily, but as the metal continues to corrode, the noise usually returns.

Leaks and corrosion (Space Saver 70B and 70F)

High-output models like the 70B and 70F tend to develop leaks at the heat exchanger joints or around the pump housing. Over time, expansion and contraction from heat cycles cause the copper joints to fatigue. Once leaks appear, corrosion accelerates rapidly, often damaging electrical components. Because most replacement heat exchangers and pump seals are obsolete, repairs are rarely long-lasting.

Circulation problems and cold radiators (Space Saver 50B, 60B, 50F, 60F)

If radiators heat slowly or unevenly, the problem usually lies with sludge accumulation or a failing pump. Mid-sized Space Saver units have smaller waterways that clog easily with iron oxide and debris. The system may also short cycle, repeatedly turning on and off as it struggles to maintain flow. Power flushing can offer a temporary improvement, but it cannot reverse internal wear in a system of this age.

Thermostat and control faults (Space Saver 70B and 70F)

Mechanical thermostats fitted to the larger Space Saver models often lose calibration, resulting in inaccurate temperature control or continuous firing. The control knobs can also seize or crack due to heat exposure. Replacement thermostats for these models are no longer produced, and adapting newer controls is complex and rarely cost-effective.

Flue and ventilation issues (All models)

Flue blockages or corrosion are common across both B and F versions. Balanced-flue systems can suffer from rusted outer cowls or partially obstructed vents, while fan-assisted flues may experience proving switch failures when the fan becomes inefficient. Restricted airflow leads to incomplete combustion and potential safety risks. Engineers generally recommend replacing these systems with modern room-sealed boilers to ensure safe operation.

General age-related faults (All models)

After more than 30 years of service, internal wiring, seals, and pipe joints have deteriorated. Small leaks, electrical shorts, and weak ignition circuits are frequent. Most original spare parts are discontinued, meaning that even when repaired, another fault is likely to follow. At this stage, full replacement is the most reliable and cost-effective option for continued safe heating.

While individual issues can sometimes be repaired, the frequency of faults and lack of genuine replacement parts mean most Space Saver B and F boilers are no longer practical to maintain. Upgrading to a modern A-rated boiler will provide immediate improvements in safety, efficiency, and reliability.