Baxi Boiler 117 Error Code: Causes & Fixes

At Boilers 2 Go, we’ve seen the Baxi boiler 117 error code crop up more than its fair share—it’s that high pressure warning that can lock out your unit, leaving you without heat or hot water when you need it most. 

If your Baxi is displaying 117 and shutting down, this guide pulls from practical fixes to explain what it signals, the common reasons behind it, and step-by-step ways to resolve each for average homeowners and landlords.

What Does the Baxi Boiler 117 Error Code Mean?

The Baxi boiler 117 error code means your system’s water pressure is too high, often above 2.5-3 bar, triggering a safety lockout to prevent strain on components like pipes and valves. From our experience with Baxi combi and system models, this code—sometimes shown as E117—protects against bursts or leaks by halting operation until pressure normalises, ensuring your central heating network doesn’t suffer damage from excessive force.

High Pressure Implications

This fault can cause noisy operation or leaks if ignored, tying into the boiler’s sensor detecting unsafe levels in the sealed loop—common in UK hard water areas where overfilling goes unnoticed.

What Causes the Baxi Boiler 117 Error Code?

The Baxi boiler 117 error code is caused by excess water pressure building in the closed circuit, often from user error or component failures overwhelming the system’s capacity. From our repairs in mineral-rich UK regions, this builds when expansion isn’t managed; here’s the key triggers with hands-on solutions.

Overfilling During Repressurising

Overfilling during repressurising causes 117 by adding too much water via the filling loop, spiking pressure beyond safe limits. Why it’s caused is accidental prolonged valve opening or faulty gauges misleading users during routine top-ups.

How to Fix Overfilling During Repressurising

1. Turn off the boiler and let it cool to avoid hot water sprays.
2. Bleed radiators starting upstairs to release excess water/pressure until the gauge drops to 1.2 bar.
3. Reset the boiler and test operation.
4. If pressure rises again, check filling loop valves for leaks—replace if dripping, or call Gas Safe for £100-£200 repair.

Faulty Filling Loop Valve

A faulty filling loop valve triggers 117 by leaking mains water into the system, gradually increasing pressure. This is why it’s caused by worn washers or seals failing from constant use or hard water scale.

How to Fix Faulty Filling Loop Valve

1. Isolate the boiler and close mains water supply.
2. Check loop hoses for drips when closed—if wet, disassemble and inspect washers.
3. Replace faulty seals or the entire loop assembly, available from plumbing stores.
4. Repressurise to 1.2 bar, reset, and monitor; Gas Safe install if unsure, £150-£250.

Expansion Vessel Failure

Expansion vessel failure causes 117 by not absorbing water expansion during heating, forcing pressure up. Why it’s caused is diaphragm rupture from age or low pre-charge air pressure in the vessel.

How to Fix Expansion Vessel Failure

1. Check vessel air pressure with a gauge when system is depressurised—if below 0.75 bar, recharge with bike pump.
2. If wet at valve (water leak sign), it’s ruptured.
3. Drain system partially to replace vessel.
4. Gas Safe handles full swap, £200-£400, then reset and test.

Faulty Pressure Sensor

A faulty pressure sensor leads to 117 by misreading normal levels as high, falsely locking out. Why it’s caused is scale buildup or electrical faults in humid environments affecting accuracy.

How to Fix Faulty Pressure Sensor

1. Reset boiler multiple times to clear glitches.
2. Repressurise if gauge shows normal but code persists.
3. Clean sensor if accessible after isolating.
4. Gas Safe replaces sensor, £150-£300, and flushes to remove scale.

Blocked or Faulty Pressure Relief Valve

A blocked or faulty pressure relief valve causes 117 by not releasing excess when needed, trapping pressure. Why it’s caused is debris jamming or wear preventing proper opening in hard water systems.

How to Fix Blocked or Faulty Pressure Relief Valve

1. Check discharge pipe for flow—if none during high pressure, it’s stuck.
2. Manually lift valve to release (wear gloves for hot water).
3. Flush with cleaner if blocked.
4. Replace via Gas Safe if faulty, £150-£250, then reset.

When Should You Get a New Boiler Quote?

If 117 keeps appearing despite pressure adjustments, or your Baxi shows other signs of age like inefficiency, it’s time to consider a replacement for reliable performance.

A new A-rated boiler ends these high pressure hassles. Request a new boiler quote from Boilers 2 Go today.

FAQs

How does water quality affect Baxi 117 frequency?

Hard minerals jam valves faster, spiking pressure—softeners extend intervals.

What preventive accessories help with 117?

Auto-filling devices maintain levels, reducing manual errors.

Are there smart monitors for Baxi pressure?

Apps alert to rises, useful for landlords.

How often to check Baxi expansion vessels?

Annually during service spots diaphragm wear.

Can adding inhibitors stop 117 recurrences?

They reduce corrosion, stabilising valves and pressure.