Ariston Boiler Error Codes [Top 8 Problems & Fixes]

Welcome to our 5-minute guide to Ariston boiler problems. Here, you’ll find a list of common faults and learn what to do when they sneak up on your boiler.

Before skipping to one of the Ariston boiler error codes we’ve listed below, please note: all repairs need to be completed by a Gas Safe engineer.

And, if you decide you’d rather invest your cash in a new boiler with a long warranty, we’d recommend using this 90-second form from Heatable to get your fixed price online, then comparing those prices with local installers.

#1 – Printed Circuit Board (PCB) Errors (Fault Code 301-307)

PCB errors are the most common of Ariston boiler problems, and the PCB is also one of the most expensive (and vital) components on your boiler. If your boiler is showing one of the following Ariston fault codes, it’s a PCB error:

• 301
• 302
• 303
• 304
• 305
• 306
• 307

Note that Ariston boiler error codes 303, 305, 306 and 307 are the most problematic — if you see these, chances are you’ll need to replace the PCB. Now, if you’re getting the Ariston 304 error, it means that more than 5 other faults have occurred in the span of 15 minutes, so monitor your display for other codes and jot them down.

What You Need to Do Next

Have a Gas Safe engineer come and assess the damage. Sometimes, weak connections and wiring to the PCB can be repaired.

If a replacement PCB is needed, you could pay upwards of £500. Unless the rest of your boiler is in perfect condition, it makes much more sense to get a quote for a brand new and efficient boiler.

#2 — Low Water Pressure (Ariston Error 108)

Now onto a less severe problem we regularly see with Ariston boilers — low water pressure. If you’ve got low water pressure, it’s likely you’ll see fault code 108 displayed on your boiler.

Water pressure is lost due to leaks. This could be via your boiler, or other parts of the heating system.

What You Need to Do Next

First, you’ll have to find and fix the leak. We’ve already created a quick guide to why boilers lose pressure here; you can also check out our guide to boilers leaking water here.

Mind you, these guides are for informational purposes — you should always hire a Gas Safe engineer to investigate and fix boiler leaks.

After the engineer takes care of the leak, they’ll need to top up the pressure to at least 1.3 bar using the external filling loop.

#3 —  Ignition Failure (Ariston Fault Code 5P1 & 5P2)

If an ignition fault is causing your Ariston boiler problems, you’ll likely see a 5P1 or 5P2 fault code show up on your display. And when your Ariston boiler isn’t igniting, it’s likely due to:

• Ignition lead or probe faults
• A blocked burner
• The pilot jet is blocked full of debris
• The spark generator isn’t working

What You Need to Do Next

With most of the Ariston boiler problems listed above, your boiler should ignite again after minor repairs.

However, if a burner is blocked and is in bad condition, you’ll need to replace it. And if your boiler is particularly old, it might be worth comparing the cost of repairs with the price of a complete replacement.

Once old boiler parts start to deteriorate, others quickly follow. And there’s little point investing lots of cash into an old boiler that’s likely to fail again (and cost you more money).

#4 – No Flame (Ariston Fault Code 501)

If there’s no pilot light in your Ariston boiler, you’ll see the 501 error code.

There are lots of potential causes, but it’s likely a blocked pilot jet. However, this isn’t an easy problem to diagnose. If you see a pilot light but are still getting the 501 fault code, the flame sensor is likely to blame.

What You Need to Do Next

To reset the 501 Ariston error, a boiler engineer will have to dismantle your appliance, clean out the pilot jet, and reinstall it.

Crucially, they’ll also check for anything else that could affect the ignition sequence and flame-sensing abilities of your boiler.

#5 – Air Pressure Switch Failure (Fault Code E34)

Ariston boiler error codes on new models differ from those the older units show. For example, the Microgenus will display an E34 code if there’s an air pressure switch failure.

The air pressure switch ensures that the fan is pushing harmful gases out of the boiler, up the flue, and out of your property. If there’s a fault with the air pressure switch, the boiler isn’t safe to operate. The PCB can’t be certain if your boiler is expelling the flue gases, so locks out just in case.

What You Need to Do Next

If you’re lucky, the fault will be limited to the air pressure switch.

But, Ariston boiler error codes aren’t always 100% accurate. The problem could be the connection between the PCB and air pressure switch, meaning the PCB is actually at fault.

When the PCB needs to be replaced on older boilers, it makes much more sense to consider getting a boiler replacement quote.

Of course, compare the cost of a repair first and determine which one makes more financial sense to you.

#6 – Insufficient Circulation (Ariston Boiler Error 103-108)

Ariston boiler problems arising from insufficient circulation will usually result in the following fault codes:

• 103
• 104
• 105
• 106
• 107

Ariston error 108 means (for all combi boilers) “insufficient water/request filling,” but could signify any of the issues that cause the above faults, and also point to a pressure sensor error. 

Now, back to circulation issues. In a boiler, these can boil down to 2 things:

• Central heating pump problems
• Blockages in the heating system

Heating Pump Problems

If the heating pump isn’t circulating correctly, radiators and hot water won’t get up to temperature. Here are some underlying causes of this problem:

• Incorrect installation (heating pumps need to be installed so the shaft is horizontal)
• Airlocks in the heating pump
• Worn bearings, or pump shaft
• Blown pump seals
• Incorrect speed setting

Blockages

Blockages in a central heating circuit typically come from heating sludge. This is a build-up of grime and rust in your pipes, radiator and boiler. It won’t allow water to circulate correctly, and it may be why the 103-108 fault codes are being displayed.

What You Need to Do Next

If you suspect a problem with the pump, refer to our heating pump problems guide here.

Where you suspect a blockage, refer to our guide on heating sludge here.

If heating sludge has built up in your boiler, a repair could fix it.

But it’s always worth considering the cost of a boiler replacement that won’t subject you to expensive boiler repairs in the future.

#7 – Fan Not Working (Ariston Fault Code A41)

When a fan stops working, a boiler becomes dangerous as it can no longer vent harmful fumes to the outdoors through the flue. If this is the problem with your Ariston boiler, it will lockout and display the A41 fault code.

What You Need to Do Next

Do not reset your boiler — this won’t fix the problem.

Instead, call a Gas Safe engineer to come and start troubleshooting the fault for you. If the fan needs replacing, it’s likely that other expensive parts are on their way out too.

In this case, we’d suggest getting a boiler replacement quote.

#8 – Insufficient Fan Speed (Ariston Fault Code 604)

Like a faulty fan, a fan that’s not turning at the correct speed is dangerous because it won’t expel harmful gases out of your home. In this case, you’ll see the Ariston 604 error on your control panel. You’ll get this fault on the following models:

• Clas Net ONE combi
• Class System ONE
• System and Combi Clas HE R
• Clas HE evo System
• Clas HE evo combi
• E-System evo
• E-Combi evo

What You Need to Do Next

The solution here is the same as above:

• Call a Gas Safe engineer to assess the damage.
• If the fan and other expensive parts need replacing, you should consider getting a quote for a replacement boiler.

How to Reset an Ariston Boiler

If the problem has been fixed, you’ll need to reset your boiler. After the reset, any red lights you may have seen should disappear.

If the red lights are still showing on your boiler, have a heating engineer check for further problems.

We’ve created a guide on how to reset a boiler here.

FAQs About Ariston Boiler Errors

Below, we’ll answer some of your most pressing questions about Ariston boiler problems.

What does SP1 error mean on an Ariston boiler?

The SP1 error (which is really the 5P1 error, though the display makes the “5” look like an “S”) means that the boiler’s first ignition attempt has failed. The most likely reasons for this error are:

• Malfunctioning ignition leads
• Debris in the pilot jet
• A burner that’s clogged
• Faulty spark generator

A heating engineer has the necessary expertise to accurately diagnose the fault and recommend a fix.

How do I fix an SP1 error on an Ariston boiler?

If you’re getting the SP1 (5P1) error on an Ariston, the engineer servicing your appliance will have to determine why the boiler isn’t able to ignite. If you’re lucky, simply cleaning out debris from the burner or pilot jet may solve the problem. Alternatively, you may have to replace the ignition leads or spark generator.

What should the pressure be on an Ariston boiler?

The optimal pressure for an Ariston is around 1.3 bar. That said, it’ perfectly normal for the pressure to rise while the boiler is heating water, so don’t panic if your pressure gauge shows 1.5-1.8 bar.

However, if you see the pressure steadily rising past 2 bar and beyond, there may be a fault with the boiler or the central heating system. You can read more about pressure problems in our guides to low and high boiler pressure.

Why is my Ariston boiler losing pressure?

Any boiler that’s losing pressure (including one manufactured by Ariston) likely suffers from a leak. The water leak isn’t necessarily in the boiler itself; it may be anywhere in the heating circuit — the radiators, pipework, or towel rails.

And whilst it’s easy enough to repressurise a boiler by topping it up with water, doing so will not solve the pressure issue unless you’ve fixed the leak first.

What’s Next?

Thanks for reading our 5-minute guide to the most common Ariston boiler issues.

Is your boiler problem not covered? Do you have more questions? Leave a comment below and we’ll get back to you as soon as possible.