Glow-worm F22: low water pressure on an Ultracom or Betacom
F22 on a Glow-worm is a straightforward low-pressure code, but the frequency it appears at matters more than the single event. A genuine one-off is very different from a boiler that needs refilling every fortnight.
Understanding a Glow-worm F22 shortage before you spend money
Refill with the boiler cold, using the external filling loop, up to the pressure figure printed on the appliance data badge, then fully close both loop valves. Where the fault returns within weeks, the search moves to the expansion vessel charge and then to slow leaks at radiator valves, pipe unions and the pressure relief valve seat, roughly in that order of likelihood.
Relevant registrations
- Gas Safe registered for domestic gas boiler work
- OFTEC registered for oil boiler work
- Worcester Bosch Accredited Installer
A Glow-worm F22 shortage — the facts that change the job
- Refill cold, to the figure on the appliance data badge, not a guess
- Close both filling loop valves fully once the target is reached
- A vessel that has lost its charge causes very frequent top-ups
- Radiator valve unions are a common slow, hard-to-spot leak point
- The relief valve seat is checked where staining appears outside
Questions we get asked
- What if I don't know the target pressure?
- It is printed on the data badge inside or beside the appliance; if it is missing, an engineer can confirm the correct figure for your model.
- Is it safe to run the boiler slightly under pressure?
- Below the manufacturer's minimum the boiler will lock out to protect itself rather than run unsafely.
Related help pages
- Symptom guideNo hot water but the heating works: what that combination means
- Leak triageWater leaking from the boiler: what is urgent and what can wait
- DiagnosticsIntermittent boiler faults: how to catch a fault that hides
- Potterton fault codePotterton E125: no ignition detected on a Promax or Gold
- Gas safetyGas tightness testing: how a suspected leak is actually checked
- Property typeHeating Georgian townhouses: tall rooms, long runs, old routes
Services that cover this
Where we deal with this
Need help with a Glow-worm F22 shortage?
In practice: One refill is routine maintenance. Repeated refills are a leak-finding job worth booking properly.
Use the enquiry form to describe the appliance, fault code and what changed before the problem started.
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