Servicing a Nefit-Bosch boiler, and reading its codes

Which Nefit-Bosch boilers I work on

Nefit is Bosch’s Dutch boiler brand, and the current range on the Nefit-Bosch site is the TrendLine II and TrendLine AquaPower Plus, the ProLine NxT, the 9700i and 9700i AquaPower Plus, and an electric Tronic Heat 3500. The earlier TrendLine, ProLine, ProLine Eco and 9000i are the previous generations, and Nefit-Bosch still publishes fault information for them.

Send me a photo of the type plate with your message; it tells me the model and the year.

How often Nefit-Bosch says to service it

The Nefit-Bosch maintenance page says at least once a year in general, and that newer models may only need it every two years according to the guideline for that model. It also says manufacturers make servicing to their instructions a warranty condition.

The boiler keeps its own count. On the TrendLine II, the installation manual says the display shows an H when the maintenance term has run out: the period the installer set, at most 24 months, or 4,000 burner hours, whichever comes first. H13 is the months; H03 is the hours. Nefit-Bosch explains that H03 replaced H13 from November 2020, because a boiler that runs a lot needs its service earlier to stop the heat exchanger fouling. It’s a reminder, not a fault; the boiler keeps working. After the service, the installer resets the counter, which is the last thing I do before I leave.

Pressure on a Nefit-Bosch

The Nefit-Bosch top-up guide says most boilers want between 1.5 and 2 bar; my pressure guide covers the same steps. If you top up regularly, Nefit-Bosch lists a leak, a failed expansion vessel or a problem with the safety valve as the likely reasons and says to have it checked.

The TrendLine II tells you about pressure in its own way. H07 means the pressure is too low, and the boiler limits its output until you bleed and top up. 2E 207 is the same thing as a blocking fault: Nefit-Bosch says to fill to 2 bar, and if it returns, to check the expansion vessel, the system for leaks and the pressure sensor.

One quirk is worth knowing if you have a ProLine. Nefit-Bosch documents a hot water and pressure complaint on the TrendLine, ProLine, ProLine NxT and ProLine Eco: while making hot water, the three-way valve can cut the expansion vessel off from the pump, the pressure dips and the boiler goes into standby. A ProLine shows 2E-207; a ProLine NxT or Eco shows 0U. Nefit-Bosch’s fix is a differential pressure regulator in the bypass, and it warns that swapping sensors won’t cure it. On one of these, that’s where I look first.

Reading a Nefit-Bosch code

Nefit-Bosch’s consumer advice for a fault is short: always contact your installer or maintenance company first. The TrendLine II manual sorts its codes into three kinds: a normal operating code, a blocking code, where the boiler waits and tries again once the cause is gone, and a locking code, where it shuts down and locks for safety. To unlock it you hold the reset button until “Reset” appears. Nefit-Bosch says the boiler then often runs normally again, but that some faults have to be fixed first.

A few from the manual and from the Nefit-Bosch fault pages, which are written for installers:

• 6A 227: not enough ionisation current after ignition, so no proven flame. Nefit-Bosch has the installer check for fouling, the gas pressure, the gas-air ratio and the ignition.
• 2U: too big a temperature difference between flow and return while heating. It applies to every Nefit HR boiler except the 9000i. Nefit-Bosch says the cause can be in the boiler or the installation, so it has the installer test the boiler first and then look at closed radiators, too little flow or a pump set too low.
• H28 on a TrendLine II: a maintenance notice that the heat exchanger may be fouled. Early software raised it falsely; the answer is an HCM update, then a check of the heat exchanger.

If your boiler is connected to the Nefit-Bosch HomeCom Easy app, it sends fault notifications with possible solutions to your phone. Whatever the code, a photo of the display and the type plate on WhatsApp is the quickest start.

What I do on a Nefit-Bosch service

I follow the inspection and maintenance chapter of the manual for the model. On the TrendLine II that means:

• Read the history first. The manual has me read the fault history from the menu and note the burner hours before I start.
• The burner and the heat exchanger are cleaned at every service. The burner comes out (it’s fragile and goes down convex side up), is cleaned with compressed air if needed, and the top of the heat exchanger is brushed and vacuumed. That’s the opposite of an Intergas, where the burner must not be cleaned, which is why I follow the manual for the boiler in front of me.
• New burner gasket, every time. The manual says the burner gasket is replaced at every service, along with every seal that’s been disturbed, and only original parts go in.
• Finish with the counter. Everything goes into the inspection and maintenance protocol, a new maintenance period is started, and I tell you what it’s set to.

The full list of what a service includes is on the boiler servicing page.

Repair, or replace?

For a fault, it’s €114.95 incl. BTW per hour, with no call-out charge, plus parts. A typical repair with a replacement part comes to around €300-€400 incl. BTW; boiler repair explains how a visit works.

Nefit-Bosch says a modern boiler lasts ten to fifteen years with good maintenance. A standard CW4 replacement is €1,995-€2,495 incl. BTW and a CW5 is €2,195-€2,795 incl. BTW, as guide prices; the fixed quote follows once I’ve seen the boiler, flue and pipework. New boiler cost explains what’s in that price, and boiler installation how the job runs.

Book a service or a repair

Send me a message on WhatsApp with your postcode, a photo of the type plate and, for a fault, a photo of the display and the pressure reading. I work by appointment, 08:00-16:00, seven days a week.

If you smell gas, leave the property and call 0800 9009 from outside. If a CO alarm goes off or you suspect carbon monoxide, get everyone outside and call 112.