Alpha E10 fault codewhat it means and how to fix it
Alpha describe E10 as the primary pressure switch operating. Refilling to their green band usually clears it, but the switch itself is on their own list of causes.
Take care
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. Refill into the upper green band, 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
Alpha are precise about this one and the precision changes what you should conclude. Their fault table gives E10 as "primary system pressure low", and the mechanism as "primary pressure switch has operated" — a switch, not a sensor reporting a number. That distinction is the whole page. A switch is a binary device: it is either made or it is not, it cannot tell the appliance how low the pressure is, and it can stick.
So Alpha list four causes and the switch is one of them, sitting alongside a leak in the system, the expansion relief valve having operated, and an expansion vessel that has lost its 1 bar charge. Three of those are the system and one is the appliance.
In practice the system is usually the answer, because a sealed heating circuit consumes nothing and a gauge that falls means water has physically left through a joint, a valve gland or the safety valve outside the wall. But when the gauge sits in the green and the code persists anyway, that is not a contradiction to argue with — Alpha publish a replacement procedure for the switch, and it is there because they expect it to fail.
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 |
| The pressure switch itself | Alpha name it as a cause and publish a replacement procedure for it. The signature is a gauge sitting healthily in the green while the appliance insists otherwise, and no amount of refilling changes anything. | Occasional |
| Expansion vessel lost its charge | On Alpha's list, and they publish the figure to check it against: a replacement vessel is charged to 1 bar before fitting. With the charge gone the vessel stops absorbing expansion, pressure spikes as the system heats, the safety valve dumps the excess outside, and the gauge 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. Alpha's own instruction is to close the tap when the pointer sits "in the upper green section just above 1 bar", so aim for the band rather than a number someone quoted you — 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 press the reset button and let go. Alpha say a locked-out boiler is cleared by pressing RESET, and they mean a press: holding it for eight seconds with no demand puts the appliance into chimney sweep mode, where it fires at a fixed output for an engineer to take readings.
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
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
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 September 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 28 September 2026
Pressure relief valve, 3 bar
PRV-3B£18–£42Plumbing merchant
Price checked 28 September 2026
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Related Alpha fault codes
- E01Get it checkedThe appliance tried to light and could not confirm a flame, so it has locked out. In winter a frozen condensate pipe is the most likely reason.Related: same brand
- E02Get it checkedThe overheat thermostat has tripped. Almost always this means water is not moving through the appliance properly rather than that it is running too hot.Related: same brand
- E16Get it checkedThe control board cannot confirm the fan is running at the speed it asked for, so it will not let the burner light. This one needs an engineer.Related: same brand
- E60Get it checkedThe appliance cannot confirm the pump is moving water. Left alone it becomes an overheat fault, so it is worth acting on promptly.Related: same brand
- E20Stop — call an engineerAlpha call this a flame sensing fault and define it as false flame detection: the appliance can see a flame while the gas valve is shut. Switch it off and call an engineer.Related: same brand
- E38Get it checkedThe burner lit correctly and then the flame signal was lost part-way through the cycle. That points somewhere different to a failure to light.Related: same brand
Own an Alpha boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
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
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.