Alpha E10 fault codewhat it means and how to fix it
System water pressure has fallen too low for the appliance to fire. Top the system back up to 1.2 bar and it will restart.
Before you start
How long has it been since you last had to top this system up?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Never, or not for over a year
Entirely normal. Top up to 1.2 bar, reset, and put it out of your mind until it happens again.
No follow-up needed. Note the date so you know the interval next time.
Every few months
More than the system should need. There is probably a slow weep somewhere, or the expansion vessel is losing its charge.
Mention it at the next service and ask for the vessel charge to be checked with the system drained down — it takes ten minutes and it is the most commonly skipped check.
Weekly, or more often than that
That is a leak of a size that will be doing damage somewhere, and every refill is putting fresh oxygenated water into the system, which produces the black sludge that wrecks pumps and heat exchangers.
Get a leak trace booked rather than continuing to top up. Check under the boiler, around every radiator valve, and the ceiling below any pipe run in the meantime.
What E10 means
E10 is Alpha reporting that the pressure transducer is reading below the minimum it will run at, which on most of the range is around 0.5 bar. A sealed heating system does not consume water, so the pressure only falls if water has physically left it — through a joint, a valve gland, the safety valve outside the wall, or because somebody bled a radiator and did not top back up afterwards. The lockout itself is protective rather than damaging: the appliance is refusing to fire a burner into a heat exchanger it cannot guarantee is full. Alpha appliances are slightly more sensitive here than some competitors because the E-Tec uses an aluminium heat exchanger, and aluminium tolerates running dry very badly indeed. That is a reason to take a repeatedly falling gauge seriously rather than to worry about the lockout.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Gradual loss over a long period | Every sealed system loses a little through valve glands and automatic air vents. Once a year is unremarkable and needs nothing but a top-up. | Common |
| Radiators bled without refilling | Bleeding takes volume out of the system. Do six radiators in an afternoon and the gauge will be visibly lower by the evening. | Common |
| An actual leak | Usually a compression joint under a floor or behind a bath panel. The clue is the rate: if you are topping up monthly, water is going somewhere. | Occasional |
| Expansion vessel lost its charge | The vessel stops absorbing expansion, so pressure spikes when the system heats and the safety valve dumps the excess outside. The gauge then reads low once everything cools. | Occasional |
What to try yourself
Read the pressure gauge with the heating off and the system cold. On the E-Tec it is a small dial on the underside of the appliance rather than on the front panel, so you may need to look up at it.
Find the filling loop. Alpha most often fit an external braided hose with a lever valve at each end, on the pipework below the case.
Open both valves slowly and watch the gauge. Close them the moment it reaches 1.2 bar — the needle moves faster than you expect in the last quarter bar.
Do not go past 2.5 bar cold. The safety valve will discharge outside and you will end up low again once it settles.Close both valves firmly, then hold the reset button for five seconds. The display should clear and the appliance should respond to a call for heat.
Write the date on a note by the appliance. Check the gauge again in a fortnight — the rate of loss is the piece of information an engineer actually needs.
Get a Gas Safe registered engineer to look at your Alpha E10
Gas Safe Register engineers only. No obligation.
What it costs to fix
Typical repair cost
£0–£450
Time on site
10 minutes
Free if it is simply a top-up. A leak trace is typically £90 to £160, and a replacement expansion vessel £180 to £450 fitted depending on access.
Typical UK prices including parts and labour, updated August 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Expansion vessel (8 litre, sealed system)
EV-8L£35–£85Plumbing merchant
Price checked 5 August 2026
Pressure relief valve, 3 bar
PRV-3B£18–£42Plumbing merchant
Price checked 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Alpha fault codes
- F.22Get it checkedThe boiler has shut down because there is not enough water in the system. Pressure has dropped below roughly 0.5 bar and it will not fire until you top it up.Related: water pressure
- F.75Get it checkedThe boiler cannot detect a rise in pressure when the pump starts, so it has locked out. Usually a failed pressure sensor or a pump that is not moving water.Related: water pressure
- F1Get it checkedSystem pressure has dropped below the minimum the boiler will run at. Topping it back up to 1.2 bar usually clears it straight away.Related: water pressure
- CE 207Get it checkedSystem water pressure has dropped too low for the boiler to run safely. Topping the system back up to 1.2 bar usually clears it in five minutes.Related: water pressure
- 108Usually simple to fixThe heating circuit does not contain enough water to run safely. Refill through the filling loop to about 1.2 bar and the code clears.Related: water pressure
- E119Get it checkedSystem pressure has fallen below the level the boiler will operate at. Refilling to 1.2 bar and resetting usually clears it in a few minutes.Related: water pressure
Related guides
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal