Overview
The E119 error on a Baxi Duo‑tec / Megaflo boiler means the boiler has detected low water pressure in the central heating system. Most Baxi combi boilers need system pressure in the region of about 1.0–1.5 bar when cold; if the gauge reads well below that the boiler will lock out and show E119. This is a common, non‑catastrophic fault and usually prevents the boiler from firing until pressure is restored. Low pressure is often caused by normal slow losses of water (for example after bleeding radiators), a small leak in the heating system (pipes, radiators or the boiler), or a problem with components such as the filling loop valves, pressure relief valve (PRV) or expansion vessel. In many cases a homeowner can safely repressurise the system using the filling loop or the boiler’s easy‑fill lever, but if the pressure drops again or you find leaks, a Gas Safe registered engineer should be called for diagnosis and repair.
Possible Cause: low water pressure error
Troubleshooting Steps
Safety precautions:
- Before doing anything switch the boiler off at the programmer and isolate electrical supply if convenient. Allow the boiler to cool to avoid hot water scalds. Treat the boiler as a gas appliance: any gas or internal repairs must be done by a Gas Safe registered engineer.
- Have towels or a container ready for a few drips when operating the filling loop. Wear eye protection if working under the boiler.
Initial checks a homeowner can do:
- Open the front flap and check the pressure gauge. If it reads below about 1.0 bar (often much lower) that will trigger E119.
- Look and feel around the boiler, pipework, radiators and under the unit for any signs of leaks, damp, corrosion or puddles.
- If you have recently bled radiators this commonly causes pressure loss and simply topping up is normal.
Specific diagnostic and fix steps (repressurise the system):
1. Turn the boiler off and let it cool a little. Confirm the pressure reading when cold.
2. Locate the filling loop: on Duo‑tec/Megaflo models this is usually underneath the boiler on the right and is either a metal/flexible hose with two isolation valves or an Easy‑Fill green lever. Remove any end caps if present.
3. If you have a green Easy‑Fill lever: push or hold the lever down to allow mains water into the system. Watch the pressure gauge and release the lever when the needle reaches about 1.0–1.5 bar (or to the top of the green area if marked).
4. If you have a two‑valve filling loop: slowly open the valves (usually both) until you hear water flow; watch the gauge and stop when the pressure reaches about 1.0–1.5 bar. Close both valves tightly when done and replace any caps.
5. After topping up, check there are no drips from the valves or fittings. Tighten gently if a small dribble appears; if the valve keeps leaking do not force it and call an engineer.
6. Reset the boiler fault per the boiler manual (often switching the boiler off for a short time then back on clears the code once pressure is correct). The E119 should clear once normal pressure is reached.
What to monitor after repressurising:
- Recheck the pressure after the system has been used (heating/hot water) and again the next day. Note whether the pressure drops significantly after heating cycles or over a few days.
- If pressure only dropped because you bled radiators, topping up once may be all that’s needed.
When to call a professional (call a Gas Safe registered heating engineer):
- The boiler will not hold pressure or E119 returns repeatedly after you have properly topped up.
- You find visible leaks (wet floors, dripping from PRV discharge pipe, wet radiators, or around the boiler).
- The filling loop valves or connections leak or will not operate correctly.
- You suspect a problem with the pressure relief valve, expansion vessel, pump or internal boiler leak.
- You are uncomfortable performing the steps or unsure about isolating the appliance.
Additional notes:
- Do not leave the filling loop open permanently; it must be closed and secured after repressurising to avoid uncontrolled flows.
- If the pressure gauge itself appears unreliable (stuck needle, inconsistent readings) an engineer should inspect and replace it if needed.
- Any internal gaswork, repairs to PRV, expansion vessel or boiler internals must be done by a qualified Gas Safe engineer for safety and warranty reasons.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Duo-tec/Megaflo.