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The Top 8 Ariston Boiler Problems [And What To Do Next]

Welcome to our 5-minute guide to Ariston boiler problems, and what you need to do next.

Below we’ve got a list of common faults.

Before skipping to the specific problem with your Ariston boiler, 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 to get your fixed price online, then comparing those prices with local installers.

#1 – PCB Errors (Fault Code 301-307)

Let’s get the most depressing problem out of the way; PCB errors. One of the most expensive (and important) components on your Ariston, is the PCB.

This is the circuit board that gives and receives signals to all electronic components in your boiler.

Without it (or, if it’s broken), your boiler won’t work correctly.

If your boiler is showing one of the following fault codes, this is a PCB error:

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

303, 305, 306 and 307 fault codes are the most problematic.

These are “main” PCB errors, so there’s a good chance the unit needs replacing.

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, this could cost 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 (Fault Code 108)

Now onto a more positive problem (if there’s such a thing) we regularly see with Ariston boilers;  low water pressure.

If you’ve got low water pressure, it’s likely you’ll see the 108 fault code 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, the leak needs to be found and fixed.

We’ve already created a quick guide to why boilers lose pressure here.

We’ve also created a guide to boilers leaking water here.

That’s for informational purposes. Boiler leaks should be fixed by Gas Safe engineers.

Once the boiler leak has been fixed, the pressure needs to be topped up to at least 1.3 bar using the external filling loop.

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

If it’s an ignition fault causing problems with your Ariston, you’ll likely see a 5P1 or 5P2 fault code.

When your Ariston boiler isn’t igniting, that’s 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

Many of the above faults will require a minor repair, and your boiler will ignite again.

However, if a burner is blocked and is in bad condition, it will need to be replaced. If your boiler is particularly old, it might be worth comparing the cost of replacement with a repair.

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 (Fault Code 501)

If the problem with your Ariston boiler is lack of flame detection (i.e. there’s no pilot light), you’ll be seeing a 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

A boiler engineer will be able dismantle your appliance, clean out the pilot jet, and reinstall it.

More importantly, they’ll be checking for anything else that could affect the ignition sequence and flame sensing abilities of your boiler.

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

Newer Ariston boilers have a separate set of fault codes to older ones. For example, the Microgenus will show 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 here is going to be limited to the air pressure switch.

But, Ariston fault codes aren’t 100% accurate. The problem could be the connection between the PCB and air pressure switch, and it’s then the PCB that’s at fault.

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

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

#6 – Insufficient Circulation (Fault Code 103-108)

If you have any of the following fault codes on your Ariston boiler, the problem stems from insufficient circulation:

  • 103
  • 104
  • 105
  • 106
  • 107
  • 108

Insufficient circulation in a boiler can be down to two things:

  • 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.

The issues causing the problem could be:

  • 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 in heating systems 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 that’s 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 replacement that won’t subject you to expensive boiler repairs in the future.

#7 – Fan Not Working (Fault Code A41)

When a fan stops working, a boiler becomes dangerous. The boiler is no longer venting harmful gases out of the flue.

If this is the problem with your Ariston boiler, it will lockout and display a A41 fault code.

What You Need To Do Next

Do not reset your boiler. This doesn’t fix the problem.

Call a Gas Safe engineer to come and start troubleshooting the problem 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 considering getting a quote for a replacement.

#8 – Fan Speed Insufficient (Fault Code 604)

Like a faulty fan, having a fan that’s not turning at the correct speed is dangerous. Gases won’t be able to escape your property.

In this case, you’ll be seeing the Ariston 604 error being displayed on your control panel.

What You Need To Do Next

The solution here is the same as above:

How To Reset An Ariston Boiler

If the problem has been fixed, you’ll need to reset your boiler. If you’ve had any red lights appearing or flashing, they should have been cleared.

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.

What’s Next?

Thanks for reading our 5-minute guide to the most common Ariston boiler problems, and what you need to do next.

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.

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    1. Ariston Error code e06.

      There could be 4 – 5 different things wrong here. The manual says to call an engineer. You should do that. The most common problems for the e06 error are the plate heat exchanger or the condensate.

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