What Baxi E118 means, and what it does not tell you
Baxi E118 is a low-water-pressure message on the boiler models that use this code. It tells you that the appliance is reporting insufficient heating-system pressure. It does not tell you where water has gone, whether there is a hidden leak or which valve you should turn.
Baxi's official error-code table describes E118 as pressure below 0.5 bar in its listed E-code model group. The same page separates newer Combi/System 2 products, which use a different set of messages. Match the full model before applying an explanation or procedure.
The fault threshold is not a recommended filling target. Raising the gauge just past the number associated with the fault is not the same as following the manufacturer's cold filling instructions. Equally, filling much higher for “extra time before it drops again” is not a repair.
The useful decisions are whether an authorised user filling procedure is appropriate now, whether you can identify it confidently, and whether this is a one-off event or part of a recurring loss. This guide helps organise those decisions without giving a universal valve sequence for different installations.
Confirm the model, code and gauge reading together
Photograph the whole fault display and the visible gauge or normal-user pressure screen. Note whether the system was cold or had recently been heating. A code remembered from yesterday and a reading taken under different conditions today should not be treated as one simultaneous observation.
Use accessible paperwork or the external identification information to obtain the full model name. Include generation numbers and words such as Compact, Combi or System. Do not remove the casing to find a serial label or assume that a similar-looking control panel means the same filling arrangement.
If the display and gauge appear inconsistent, report both. Do not add water solely because the code remains while the gauge already appears at the level specified by the user instructions. That disagreement needs assessment rather than another attempt to force the message away.
Keep E118 distinct from E119. Our Baxi E119 guide addresses that separate model-family enquiry. Both may lead readers towards low-pressure information, but a different code or appliance generation is a reason to check the instructions, not to assume every control operates identically.
First rule out a situation that needs urgent help
If there is a gas smell, suspected fumes or a carbon-monoxide alarm, stop treating this as a routine pressure problem. Leave the affected building, avoid flames and electrical switching, and obtain emergency help from a safe location. Seek urgent medical attention if anyone is unwell.
The HSE domestic gas guidance gives the Great Britain emergency gas number as 0800 111 999. An appliance suspected to be unsafe must remain unused until checked. A water-pressure fault on the screen does not rule out a separate safety problem.
A substantial active water leak, water entering electrical equipment or a falling ceiling also requires urgent attention. Keep people away and report the location and visible damage. Do not repeatedly replenish a system while water is visibly escaping into the property.
Where there is no emergency, it is reasonable to obtain the correct user instructions or help with filling. Keep the appliance casing closed and leave internal valves, wiring and safety devices untouched. A normal homeowner filling operation must not become an improvised internal repair.
Find the instructions for your actual filling arrangement
Baxi's pressure top-up guidance asks owners to watch the relevant instructional video fully before attempting the task. It also says its support service or a registered engineer can help if the owner cannot manage or would prefer assistance. There is no need to guess under time pressure.
Compare the instruction with the controls you can actually see. An integrated filling device and an external loop should not be treated as interchangeable. If the illustrated arrangement does not match, obtain the correct guidance rather than deciding that the nearest pair of valves must be equivalent.
Before starting any permitted procedure, identify its stopping point and how the filling controls are returned to their normal closed state. If you cannot read the gauge while reaching the controls, cannot operate them comfortably or do not understand the sequence, arrange help.
Do not force a stiff handle, use pliers on a user control or operate an unidentified valve because its colour resembles one in a video. A clear photograph sent to manufacturer support or the installer is more useful than trial and error beneath the boiler.
Use the specified target and stay with the task
Follow the exact user instructions for system temperature, target pressure and control operation. Read them all before beginning. Different installations and gauges can look similar while requiring different handling, so this page deliberately does not substitute one universal numerical target.
Observe the gauge throughout the permitted filling operation. Do not leave a filling control open while answering the door, collecting another tool or waiting to see whether the heating starts. If you cannot supervise the task, stop it using the identified procedure and seek assistance.
When the specified target is reached, finish the procedure completely, including returning the identified filling controls to their required position. Record the final reading and time. Do not leave the arrangement in a filling state to compensate for a known pressure loss.
If the user instructions require a further normal-user step, follow that instruction. Do not repeatedly reset the appliance or enter a service menu merely because E118 remains on the screen. A persistent message after the specified procedure should be reported with the gauge reading.
Stop if pressure does not respond as expected
If the gauge does not rise during the instructed operation, stop rather than progressively opening more valves. You may not have identified the correct arrangement, or another issue may need attention. The absence of an expected response is a reason to reassess, not permission to improvise.
If water starts leaking from the filling arrangement, pressure rises unexpectedly quickly or you are unsure whether the controls are closed, end the attempt through the known procedure where you can do so safely and call for help. Describe what you operated and the current reading.
If you have exceeded the specified target, do not create another problem by opening an unknown drain or operating a safety valve. Seek model-specific advice. Tell the engineer or support service the highest reading observed and whether it changed after filling stopped.
Honesty about an unsuccessful attempt helps diagnosis. Take an accessible photograph showing the arrangement and explain the sequence without removing anything. You do not need to conceal a mistake or restore an imagined original position by guessing.
One low reading and repeated replenishment need different follow-up
A low-pressure event after documented heating work has useful context: water may have been drained, radiators changed or the system handed back with instructions for follow-up. Contact the contractor with the reading and timing rather than assuming that hidden pipework suddenly failed.
Recurring E118 is a different complaint. Record how often it returns and what happened between episodes. “Three times this month” is more useful than “occasionally”, while an exact diary is better still when available. Do not keep filling indefinitely instead of investigating the recurrence.
The fact that topping up temporarily restores operation does not establish the source of the loss. It only records the result of adding water under those circumstances. A lasting repair requires understanding why the condition returns.
Tell the engineer about previous internal repairs and any earlier leak investigation. Keep the findings rather than just the invoices: knowing that a component was replaced is different from knowing what cause was identified and whether the loss was subsequently checked.
Make a pressure diary that an engineer can interpret
Use readings taken under comparable conditions wherever possible, without deliberately running a faulty appliance. For example, record an ordinary cold reading before the scheduled heating starts and note any later reading separately as warm or recently operated.
| Record | Useful entry | Avoid |
|---|
| Date and time | Timestamp linked to a photograph | Several unlabeled gauge images |
| System state | Cold, recently heated or unknown | Comparing unlike conditions as a precise loss rate |
| Pressure | The visible value or a clear gauge image | Guessing more precision than the gauge provides |
| Filling | When performed and final recorded reading | Omitting top-ups from the timeline |
| Water observations | Accessible drip, stain or discharge location | Calling every wet pipe a heating leak |
The diary does not need dozens of readings each day. Its purpose is to preserve a pattern and relevant interventions, not to make the occupant continuously monitor the boiler. Ask the engineer what further information would be useful for the particular complaint.
Do not calculate litres lost from the gauge movement alone. A pressure change is not a household water-meter reading, and the installation needs assessment before converting observations into a theory about the size or location of a leak.
Look for accessible evidence without opening the building
Baxi's low-pressure FAQ describes several possible causes, including heating-system leakage, expansion-vessel issues and pressure-relief-valve discharge. It notes that a small leak may leave staining or corrosion without an obvious puddle. Internal components require an appropriately qualified engineer.
From safe, accessible positions, note visible staining around radiator valves, damp beneath an exposed pipe joint or a drip that can be photographed. Avoid touching hot components, tightening joints or removing floor coverings to confirm a suspicion.
If there is an external discharge, record where it is and when it was noticed. Do not cap, block or alter the pipe. A photograph helps an engineer identify what it serves; not every pipe outside the home belongs to the heating circuit.
Absence of visible water does not prove that there is no loss, but it also does not justify declaring a hidden leak. The next assessment should consider the appliance and accessible installation before authorising a search beneath finished surfaces.
Understand the engineer's first findings before choosing leak detection
A useful report distinguishes the low-pressure symptom, the observed cause where established and any unanswered question. Ask whether the findings concern an internal appliance component, visible connected pipework or an unresolved loss requiring further investigation.
If the proposal is to replace or service an internal component, ask what supports it and what follow-up will assess the pressure behaviour. If the proposal is to trace pipework, ask what evidence points away from the appliance and towards that circuit.
Do not treat a statement that the boiler was running at the end of a visit as a complete explanation of recurring pressure loss. It is one result. The job record should also identify what was corrected or why the engineer needs more evidence.
Where the first assessment is inconclusive, agree the next question and the scope of further work. That is more useful than booking several contractors with the same vague instruction to “stop the pressure dropping” and no shared account of completed checks.
If you rent, share the evidence through the repair route
Send the landlord or housing provider the exact code, model if known, pressure photograph and any recurring pattern. Use the emergency repair route where there is urgent damage or a safety concern, and explain the effect on heating, hot water and vulnerable occupants.
Ask for instructions before undertaking an unfamiliar filling operation. Do not access locked communal equipment or another flat's services to find a presumed filling valve. A provider should be told when the instructions supplied do not match the visible installation.
Keep the repair reference and contractor's outcome together with the pressure diary. If E118 returns, update the same report with the new occurrence rather than starting a disconnected complaint that omits earlier findings.
For managing agents coordinating several contractors, send the actual findings between visits. A boiler inspection, a visible radiator repair and a hidden-pipe investigation are different scopes. The next contractor needs to know which questions have already been answered.
Book the right help for recurring E118
If you need help with the filling controls or suspect an internal boiler issue, use the manufacturer support route or a suitably qualified boiler engineer. Explain whether E118 is new, recurring, accompanied by a different reading or still present after the correct user procedure.
For a separate, supported heating-pipework loss, send us the pressure history, engineer's report and photographs of accessible damage. Our heating-water leak service covers investigation, pipework repair and making good necessary access. We do not use a low-pressure code alone as proof that floors need opening.
Leak Fix London's water-leak rate is £150 per hour. If we do not find the leak, you do not pay for the time spent looking. Read the pricing and scope; this is an hourly service rate, not a fixed price for every E118 complaint or an internal boiler repair.
If the message changes, retain the new code. Our E110 overheat guide and E125 circulation guide address different faults. Resolving low pressure should not cause another reported problem to be overlooked.
