Error 2970 B

Safety first

1) If you smell gas, immediately leave the property and call the gas emergency number—do not attempt any checks. 2) Turn off the boiler before you begin any work: use the boiler isolator switch or the fused spur. Allow the boiler to cool. 3) Have towels and a bowl ready before working with valves or the filling loop to catch escaping water. 4) Do not block or cap the pressure relief/overflow pipe if it is discharging; this is a safety outlet and must remain open.

Initial checks a homeowner can do

1) Read the pressure gauge on the boiler. If it is below about 1.0 bar (cold) the system is under‑pressurised. Normal cold pressure is around 1.0 bar and when heating is running typically 1.5 bar or a little higher. 2) Visually inspect for obvious leaks: look under the boiler, around radiators (valves, bleed points), visible pipe joints and any exposed pipework. Check floors and walls for damp patches. 3) Check the external PRV discharge pipe (usually a plastic pipe running from the boiler to the outside); look for dampness or drips which indicate the PRV is releasing water. 4) If it is cold weather, check for frozen condensate pipe: a frozen condensate can cause fault conditions and pressure/release issues.

Repressurise the system (homeowner DIY if you are confident)

1) Identify your filling loop type: external flexible hose with two valves, an internal keyed filling link, or a keyless blue lever. If unsure, consult your manual or Worcester Bosch videos. 2) With the boiler off, open the filling loop carefully (follow your boiler instructions): for external loop attach hose and open mains tap then the loop valve; for internal keyed turn the key; for keyless pull the blue lever. 3) Watch the pressure gauge and stop when pressure reaches about 1.0–1.5 bar (aim for just over 1.0 bar cold). 4) Close the valve(s) fully and, if using an external loop, remove and store the hose. Wipe up any drips. 5) Turn the boiler back on and monitor pressure over the next hours/days. If pressure rises above safe limits, isolate water and call an engineer.

Bleeding radiators and short checks

1) If you have recently bled radiators, the pressure will drop and you will need to repressurise. Bleed radiators carefully and then top up the system. 2) Bleed radiators to remove trapped air (which can cause erratic pressure and poor circulation). Repressurise afterwards. 3) If bleeding a radiator causes a large pressure drop that rapidly recurs, suspect a leak.

Diagnostic steps if pressure keeps dropping

1) After repressurising, monitor the gauge over 24–72 hours. Note whether the drop is gradual or rapid and whether it drops only when the system is cold or when heating is on. 2) If pressure falls as soon as the system heats up, suspect the expansion vessel or PRV. 3) Check the PRV discharge pipe for fresh water after a heating cycle. Continuous dripping indicates a leaking PRV or excessive system pressure forcing discharge. 4) Look for hidden leaks: check under flooring, cupboards, around boiler flanges and any visible pipe runs. Even small, hard-to-see leaks will eventually cause repeated pressure loss.

When NOT to DIY and when to call a professional

1) Call a Gas Safe registered engineer if: you cannot find the leak after visual checks; pressure keeps dropping after repeated repressurising; the PRV appears to be discharging; you suspect the expansion vessel has lost its air charge; you see water under the boiler or signs of corrosion; the fault code persists after repressurising or the boiler locks out repeatedly. 2) Any internal boiler repairs, replacement of PRV, expansion vessel, pressure sensor, pump work or gas-side interventions must be performed by a qualified engineer. 3) If you are unsure how to operate the filling loop or worried about working on the system, stop and call a professional.

Additional notes and practical tips

1) Try a simple power reset (turn off, wait 30 seconds, turn on) only after addressing pressure—sometimes the code clears if it was a temporary sensor anomaly, but if underlying pressure loss hasn’t been fixed the fault will return. 2) Keep a log of pressure readings and any times you top up—this helps an engineer find intermittent leaks. 3) Do not seal or modify PRV discharge pipes; if the PRV is faulty it needs replacement by a Gas Safe engineer. 4) If you suspect a frozen condensate pipe in cold weather, thaw with warm (not boiling) water or a warm cloth; do not use open flame or excessive heat.

Summary

You can safely carry out visual checks, bleed radiators and repressurise the system to about 1.0–1.5 bar yourself. If pressure drops again quickly or you find signs of leaking or PRV discharge, stop and arrange for a Gas Safe registered engineer to diagnose and repair (expansion vessel, PRV, pressure sensor or internal boiler work). Prompt action prevents damage and loss of heating/hot water.