Keston E37 Fault Code: Causes, Fixes & Repair Costs
What does the Keston E37 fault code mean?
The E37 code appears on Keston boilers when the control system detects that the central heating water pressure has dropped to an unacceptably low level. The boiler monitors pressure continuously and will display E37 — typically alongside a flashing display — when pressure falls below roughly 0.5 bar, which is well beneath the safe operating range. The fault essentially tells you two things: check the system pressure, and consider whether the pressure sensor itself may be at fault. In most cases the fix is straightforward repressurisation via the filling loop, but if the boiler keeps losing pressure or the error persists after topping up, a Gas Safe registered engineer should investigate further. You can view the live pressure reading on a Keston boiler by pressing the 'Installer' button on the fascia repeatedly until '5' appears on the display — after a few seconds the screen shows the current pressure in bar.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Low system water pressure (no underlying leak) Common
Over time, all sealed heating systems slowly lose a small amount of water through micro-permeation and routine radiator bleeding, causing pressure to drop. If the gauge reads below 1.0 bar and the boiler hasn't been losing pressure rapidly, simply topping up via the filling loop is usually all that's needed. A reading around 0.5 bar is the typical trigger point for E37 on Keston boilers.
- Water leak somewhere in the heating system Common
A leak at a radiator valve, pipe joint, or around the boiler itself causes ongoing and repeated pressure loss. If you find yourself topping up every few days or weeks, suspect a leak. Look for damp patches on floors, wet spots around radiator valves, or visible drips beneath the boiler. Do not just keep topping up — a persistent leak needs professional diagnosis and repair.
- Faulty or recently bled radiators Sometimes
Bleeding radiators releases water along with trapped air, which can drop system pressure enough to trigger E37. This is a very common and innocent cause — if you bled radiators recently and the fault appeared shortly after, a simple top-up should resolve it.
- Pressure relief valve (PRV) weeping or discharging Sometimes
The PRV is a safety device that opens to release water if pressure gets too high. If the PRV seat has deteriorated it may weep continuously, slowly draining the system. Look for a damp or discoloured pipe leading outside or to a drain. A weeping PRV needs replacing by a heating engineer.
- Faulty water pressure sensor Rare
If the system pressure is correct (1.0–1.5 bar) but E37 persists, the pressure sensor itself may have failed and is sending the boiler an incorrect low-pressure signal. Replacement sensors are relatively inexpensive (around £15–£30 for the part), but fitting requires a qualified engineer.
How to fix it
- Check the system pressure reading on the boiler DIY safe
Press the 'Installer' button on the Keston fascia repeatedly until the digit '5' appears, then wait a few seconds — the display will switch to show live system pressure in bar. Alternatively, look for the pressure gauge on the front of the boiler. A healthy reading is 1.0–1.5 bar when the system is cold. If it shows below 1.0 bar (and especially around 0.5 bar), low pressure is confirmed as the likely cause of E37.
- Check for obvious leaks before topping up DIY safe
Walk around your home and inspect visible radiator valves, pipework joints, and the area directly beneath the boiler for any signs of dripping water or damp marks. If you find an active leak, do not top up the system — contact a Gas Safe registered engineer to locate and repair the leak first. Topping up while water is escaping wastes water, can cause damage to building fabric, and won't resolve the fault.
- Repressurise the system via the filling loop DIY safe
Locate the filling loop — typically a short flexible braided hose with one or two small valves, found beneath the boiler. Slowly open the valve(s) to allow mains water into the heating circuit, watching the pressure gauge (or the boiler display reading) rise. Stop when it reaches 1.5 bar and close the valve(s) firmly. Do not overfill: pressure above 2.5–3 bar when cold can cause the PRV to discharge. Once complete, check that both filling loop valves are closed completely to prevent an unintended mains water connection.
- Reset the boiler and monitor DIY safe
Press and hold the Reset button (refer to your Keston manual for the exact location — it is usually on the fascia) until the boiler attempts to restart. Allow the boiler to fire and run through a full heating or hot water cycle, then re-check the pressure after 20–30 minutes. If pressure holds steady around 1.0–1.5 bar and E37 does not return, the fault is resolved. Reset the boiler no more than two or three times in total — repeated resets without resolution indicate a deeper problem.
- If E37 returns or pressure keeps dropping, call a Gas Safe registered engineer Gas Safe engineer
A recurring E37 fault after repressurisation almost always points to either a leak somewhere in the system or a failing pressure sensor. A Gas Safe registered engineer will pressure-test the system to locate leaks, inspect the pressure relief valve for weeping, and test or replace the pressure sensor if needed. You can verify any engineer's credentials at GasSafeRegister.co.uk or by calling 0800 408 5500.
Parts you may need
- Water pressure sensor · from £25
- Pressure relief valve (PRV) · from £35
- Filling loop assembly (replacement) · from £20
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £80–£280, depending on the underlying cause.
Frequently asked questions
Can I fix a Keston E37 fault myself?
In many cases, yes — if the cause is simply low system pressure with no underlying leak, topping up via the filling loop is a straightforward homeowner task. However, if the pressure keeps dropping, if you spot any water leaks, or if E37 returns after topping up and resetting, you'll need a Gas Safe registered engineer to investigate. Work on the pressure sensor, PRV, or any gas or electrical components must always be carried out by a qualified professional.
What pressure should my Keston boiler be set to?
When the system is cold, the ideal pressure is between 1.0 and 1.5 bar — with 1.2–1.3 bar being a good target. Pressure will rise slightly (typically to around 1.5–2.0 bar) when the system is hot, which is normal. If you see the needle above 3 bar when cold, or if the PRV keeps discharging water, call an engineer rather than continuing to use the boiler.
Why does my Keston boiler keep losing pressure and showing E37?
Repeated pressure loss almost always means water is escaping from the system somewhere. Common culprits include a weeping pressure relief valve, a small leak at a radiator valve or pipe joint, or a failed pump seal. In rarer cases the expansion vessel may have lost its charge, causing pressure to spike and the PRV to release water. An engineer can pressure-test the system, check the expansion vessel, and pinpoint the source of the loss. Avoid repeatedly topping up without finding the cause.
How much will it cost to fix a Keston E37 fault?
If you can top up the pressure yourself, the cost is nothing. An engineer callout to repressurise and reset typically costs £80–£150 including labour. Replacing a faulty pressure sensor adds around £15–£30 for the part, bringing the total to roughly £100–£200. A pressure relief valve replacement usually comes in around £150–£250 including parts and labour. If a leak is found and needs repairing, costs vary widely depending on location and access, but most straightforward pipe or radiator valve repairs fall in the £150–£280 range. Major leaks behind walls or under floors can cost considerably more.