Vaillant Boiler F83 Fault Code
The Vaillant fault code F83 boiler sensors detecting insufficient temperature increases problem Q & A or require an engineer for an emergency boiler repair.
The Vaillant Boiler Fault Code F83 Error Common Q&A
Vaillant Boiler F83 Fault Code
- What does the Vaillant boiler F83 fault code mean?
- What can cause the F83 error code to be displayed on my boiler?
- What do the NTC thermistors do?
- How will a boiler engineer know if the NTC thermistors are out of calibration?
- What causes NTC thermistors to lose calibration settings?
- Is there anything else that can cause an NTC thermistor to show the wrong resistance reading?
- What needs to be done about water damage, and to fix the F83 fault?
- What causes low system pressure and boiler leaks?
- My boiler only half heats radiators and hot water, what could be the cause?
- What can be done to fix the limescale problem and stop the F83 fault code appearing?
- How will a boiler engineer check for loose and damaged connections?
- What needs to be done to fix damaged or loose connections?
- How does low heat input to the heat exchanger cause the F83 error code to be displayed?
- What can be done about a faulty gas valve?
- How does a combustion chamber loose its ability to transfer heat?
What does the Vaillant boiler F83 fault code mean
According to Vaillant, the F83 fault code relates to sensors detecting insufficient temperature increases, after the burner has been lit.
What can cause the F83 error code to be displayed on my boiler
There are various problems that can cause the F83 fault code to occur. Vaillant lists the following problems:
- An incorrect resistance reading due to incorrect calibration of the NTC thermistors
- Connections between the PCB and NTC thermistors are damaged
- Low heat input into the heat exchanger
- Low water pressure
What do the NTC thermistors do
The NTC thermistors monitor the temperature of the flow (hot water out) and return (water coming back to the boiler) pipes. The temperature will differ as radiators, towel rails and pipework absorb some of the heat.
So, naturally the return NTC thermistor will read cooler than the flow.
However, they still need to be within a working range for the boiler to work. If they’re not, the boiler will lockout and display a fault code; such as the F83.
NTC thermistors measure resistance. The higher the temperature, the lower the resistance reading. And vice-versa.
This reading is transmitted back to the PCB which then calculates the temperature.
How will a boiler engineer know if the NTC thermistors are out of calibration
At 20C, the resistance reading should be 12K ohms.
A qualified boiler engineer will be able to test temperature, and test resistance.
If the reading isn’t 12K ohms at 20C, then the calibration of the NTC thermistors is incorrect, and this is going to cause problems with your Vaillant boiler.
What causes NTC thermistors to lose calibration settings
Old age and water damage is a common killer of electrical components. If the NTC thermistor isn’t giving the correct resistance readings, they can be replaced.
And the cost to replace them (parts only) isn’t particularly expensive. Thermistors (depending on the exact model of your boiler) could be as little as £30 each.
However, it’s important to test all connections and wiring.
NTC thermistors from shops selling boiler spares won’t come with fresh wiring. So, if it’s in fact the wiring or connections causing the problems, a new NTC thermistor won’t fix the problem.
Is there anything else that can cause an NTC thermistor to show the wrong resistance reading
Given another potential cause offered by Vaillant is low system pressure, you shouldn’t count out the fact that you may have a boiler leak.
This water could’ve dripped onto electrical components and damaged them. This in turn, could make the thermistors produce the wrong readings.
As we’ve mentioned, the NTC thermistors are not particularly expensive. But, if they’ve been water damaged, there’s a bigger problem at hand.
There’s a good chance that water has made its way to the PCB, and this is not as cheap to fix. A new PCB unit could cost £400 or more to replace.
What needs to be done about water damage, and to fix the F83 fault
If you’ve noticed low system pressure (there is a pressure gauge on your boiler), there’s a chance there’s a leak. In fact, if you notice pressure consistently dropping, that’s almost a guarantee of a leak.
Don’t keep topping up your boiler with the filling loop. This water is escaping. A best-case scenario is it’s not leaking within the boiler, but from pipework (but even that can cause damage).
If you’ve noticed drips or pools of water below your boiler, you can almost guarantee the leak is coming from the boiler rather than elsewhere.
And, that means there’s a good chance it’s settling on electrical components and causing damage.
The leak needs to be fixed, before fault finding all electrical components.
What causes low system pressure and boiler leaks
Central heating systems will lose tiny amounts of pressure over time.
But anything noticeable (i.e. drops in pressure over weeks or days) signifies the system has a leak.
These leaks can come from anything connected to the heating system such as:
- Filters (magnetic boiler filters, and scale reducers)
- Radiators and towel rails
- Radiator valves
- Pipework
- Boiler parts (such as the pump and heat exchanger)
- Any connections in the heating system (pipework joints, connections to the boiler etc)
Although low system pressure is listed as a potential fault connected with the F83 fault code, it’s rarely the only fault.
My boiler only half heats radiators and hot water, what could be the cause
Another NTC thermistor related issue is limescale build-up. Typically, this will result in higher temperature readings than are representative of overall water temperature, but it can go both ways.
When limescale builds up on any heating system component, it will usually create a hotspot. So, if it builds up on the NTC thermistor, it will show an elevated temperature (due to the hotspot), even though the average water temperature will be much lower.
The most common symptom here is a boiler that only half heats water or radiators, and then locks out.
Basically, the boiler thinks it’s gotten water to the desired temperature. It will either shut off, or if the NTC thermistors show signs of overheating, the boiler might lockout.
What can be done to fix the limescale problem and stop the F83 fault code appearing
If your system is old and hasn’t been cleaned out, you’ll need it flushed out with cleaning chemicals.
Once this is done, the system needs to be dosed with heating inhibitor to break down particles in the water. These particles that contribute to limescale can then be removed by fitting a scale reducer.
How will a boiler engineer check for loose and damaged connections
Although a boiler engineer can use a multi meter to test all the connections to and from the NTC thermistor and PCB, that’s not always needed. The connections and wires that are causing problems are usually visible.
It will be obvious which connections are loose. And typically, damaged connections will be connected to old and frayed wiring.
What needs to be done to fix damaged or loose connections
Loose connections are cheap and easy to fix. The engineer will need to secure all connections. Then, they’ll need to retest connections and wiring with a multi meter to ensure the problem has been fixed.
Damaged wiring can rarely be repaired (at least, in a cost-efficient manner). So, it’s wise to have sections of wiring replaced if they are the issue.
How does low heat input to the heat exchanger cause the F83 error code to be displayed
When the heat exchanger isn’t being supplied with sufficient thermal performance there’s usually two culprits:
- A faulty gas valve
- Lack of thermal transfer from the combustion chamber
What can be done about a faulty gas valve
A gas valve that is faulty or not correctly adjusted won’t be providing sufficient fuel to the burner and therefore, the heat exchanger.
A boiler engineer will first need to check adjustment. Then, they’ll need to check that the gas valve is opening and closing when it should.
Like all components on a boiler, the gas valve communicates with the PCB. If it’s faulty (or there’s damaged wiring/connections) the signals to and from the PCB will be intermittent.
So, it might be closing too early and therefore, not providing enough fuel to the burner.
On some occasions, the gas valve can be adjusted. But, a faulty gas valve will need to be replaced to fix the F83 fault code.
It’s important that the diagnosis is 100% correct. A gas valve replacement could cost £300+ including labour.
How does a combustion chamber loose its ability to transfer heat
If there’s a build-up of debris (such as carbon) in the combustion chamber, this will reduce its ability to transfer heat.
This is not common, as it takes years for this kind of build-up to really affect a boiler. And, given newer boilers are extremely efficient, this is only something that tends to happen with much older boilers.
Other Vaillant Fault Codes And Error
If your looking for the list of error codes relating to the Vaillant boiler then please read the article Vaillant Boiler Fault Codes And Cures