What SP2 means on an Ariston boiler
SP2 tells you the boiler's second attempt to light the burner has failed. Ariston's E-Combi One LPG design, installation and servicing instructions for Great Britain and Ireland list it as "2nd Ignition Failed", and the Clas One installation and servicing instructions for the 18 to 35 models give the same English wording. The French table in the Clas One manual puts it as a failed second attempt at ignition, so there is no doubt about the meaning.
Like SP1, it is a warning rather than a lockout, but it carries more weight. One failed attempt can happen to any boiler. Two in a row suggests something is consistently stopping the flame from forming.
SP2 at a glance
| Question | Answer for SP2 |
|---|---|
| How Ariston prints it | 5 P2 (the 5 looks like an S on the display) |
| Code group | 5: ignition and flame detection |
| Type | Warning (the letter P), not a shutdown |
| Comes after | SP1, the first ignition failure |
| Can lead to | 501, no flame detected, which needs RESET |
| Models documented | E-Combi One LPG 24 and 30, Clas One and Clas One System |
Why a second failure matters
Ariston's tables do not give a cause for SP2, but the sequence tells its own story. The boiler tried once, logged SP1, tried again and failed again. If the problem was a brief dip in gas or a pocket of air in the pipe, the second attempt would normally succeed. When it does not, the cause is more likely to be something that persists between attempts, such as no gas reaching the burner, no spark, or a flame that forms but is not sensed.
That does not mean the boiler is badly broken. A meter with no credit or an empty LPG bottle produces exactly this pattern. It does mean it is worth checking rather than ignoring.
Patterns worth noting
When SP2 shows up gives useful clues, both for you and for an engineer.
Only on the first start of the day
If SP2 appears in the morning but the boiler then runs all day, the ignition parts may be getting weak. A worn electrode or a tired spark generator often struggles most from cold.
Only in frost
If the warnings come with freezing weather, check the condensate pipe outside. A frozen pipe can stop many condensing boilers lighting, and our frozen condensate pipe guide shows how to thaw it safely.
After gas work or a meter change
Air left in the gas pipe can cause several failed attempts before the boiler lights. If the warnings fade over a day, that was probably the reason.
On an LPG boiler, getting worse over weeks
On an E-Combi One LPG, rising numbers of failed attempts can line up with a bulk tank running low. Check the tank gauge.
Safe checks in order
- See whether the hob or any other gas appliance lights. If not, the problem is the supply to the house.
- Check prepayment meter credit, including emergency credit.
- Look at the gas isolation valve under the boiler: the handle should be in line with the pipe.
- On LPG, check the bottle or tank level and that the supply valve at the tank or bottle is open as your supplier showed you.
- In freezing weather, check and thaw the outside condensate pipe.
- If the boiler has locked out with 501, press RESET once after these checks. Stop after two or three attempts in total.
What not to do
- Do not keep pressing RESET while SP2 is showing. It is a warning, the boiler is already retrying, and more than five resets in 15 minutes brings up error 304.
- Do not remove the front panel to watch the burner or check the spark.
- Do not tap or adjust the gas valve or the pipe joints under the boiler.
A gas smell changes everything. Do not reset or switch anything near the boiler. Turn off the gas at the meter if it is safe, ventilate and call the National Gas Emergency Service on 0800 111 999, or your LPG supplier's emergency line if you use LPG.
What a Gas Safe registered engineer will look at
If your supply is fine and SP2 keeps appearing, book a Gas Safe registered engineer. They will usually check the gas pressure at the boiler during ignition, inspect the ignition electrode and its gap, test the ignition lead and spark generator, check the condensate trap and look at the flue and air supply. If those all pass, the gas valve and control board come next. These are all inside the sealed boiler, so leave the casing on.
Give them the pattern you noticed above, how many times you have seen SP2 in a week and whether it has ever ended in a 501 lockout. That narrows down the testing and can save time on the call-out.
Typical repair costs in the UK
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £60 to £150 |
| Ignition electrode | Typically £90 to £180 |
| Ignition lead or spark generator | Typically £100 to £200 |
| Gas valve replacement | Typically £180 to £350 |
| Annual boiler service | Typically £80 to £150 |
A worn electrode found at a routine service is far cheaper and less disruptive than a lockout in the middle of winter. See our Ariston fault codes overview for the other codes in the ignition group.