Baxi 433 Boiler Fault Code
Here, we're going to discuss the 433 fault code on the Baxi boiler. Emergency Boiler Repair..
The Baxi Boiler Fault Code 433 overheat error Common Q&A
Just below, we have a list of common questions relationing to the 433 fault code on the Baxi boiler.
- What does the 433 fault code mean on my Baxi boiler?
- Will resetting my boiler fix the 433 fault code?
- What causes the heat exchanger to overheat in a boiler?
- What is heating sludge, and how could this contribute to the 433 fault code being displayed on my Baxi boiler?
- Can heating sludge be removed from the heating system and heat exchanger?
- What is limescale and how would that affect the heat exchanger?
- What can be done to remove limescale, and protect my Baxi boiler in the future?
- What does the NTC thermistor have to do with the 433 fault code on my Baxi boiler?
- My boiler engineer thinks the heating pump is the cause of the 433 fault code, how can this be?
- If the pump on my boiler needs replacing, how much is it likely to cost?
- What does the PCB have to do with the 433 fault code on my Baxi boiler?
- If the PCB is at fault, how much is it going to cost to replace?
What does the 433 fault code mean on my Baxi boiler
The 433 fault code on Baxi boilers is an overheat error.
The boiler’s printed circuit board (PCB) has noticed that the heat exchanger has exceeded its maximum temperature (95 degrees), so it locks out and displays a fault code.
The lock out in this case is protecting the heat exchanger. If the boiler kept operating, there’s a good chance that the heat exchanger would crack. That would mean that a replacement is needed, and that could cost hundreds of pounds.
This would lead to not just inefficient heating of water via the heat exchanger, but also a leak. And, internal boiler leaks can cause massive amounts of damage.
Will resetting my boiler fix the 433 fault code
Resetting your Baxi boiler won’t fix the 433 fault. However, it might fool the boiler into fixing the problem is fixed temporarily.
Once the PCB notices that the problem is still present, it will lock out again. The issue here is, the small amount of time that the boiler is running for, might cause damage to the heat exchanger.
For this reason, don’t attempt to reset your boiler. Instead, call an emergency boiler repair engineer to come and fix the problem. Once the problem has been rectified, they’ll reset your boiler for you.
What causes the heat exchanger to overheat in a boiler
There are few potential causes for a heat exchanger overheat. Starting with the heat exchanger itself, your heating repair engineer will check for:
- Heating sludge build-up
- Limescale
If they don’t find any evidence of either heating sludge or limescale, they’ll then look at:
- The flow NTC thermistor
- Heating pump (circulation fault)
- PCB
What is heating sludge, and how could this contribute to the 433 fault code being displayed on my Baxi boiler
Heating sludge is a common killer of heating systems. It’s formed from minerals in water, combined with rust that comes from towel rails, radiators and even the inside of copper pipe work. As water passes through the heating system, it breaks off small pieces of this rust, eventually creating thick, black heating sludge.
This sludge can block parts in the heating system; everything from radiator valves through to the heat exchanger. However, it’s more common that the rust that hasn’t been yet broken down into sludge, is what is blocking up parts in your boiler.
In the case of the heat exchanger, this heating sludge is going to restrict the flow of water, and that’s going to mean that water overheats. This can quickly lead to a temperature of over 95 degrees, at which point the boiler will lock out and display the 433 fault code.
Can heating sludge be removed from the heating system and heat exchanger
Heating sludge can be removed, if it’s not set solid on parts such as the heat exchanger.
The first thing your boiler repair engineer will need to do, is hot flush the system using chemicals such as central heating inhibitor. The combination of heat and chemicals will break down this heating sludge, so it can be flushed from the system.
But, that’s not enough to protect the heating system in future. Sludge will continue to build-up over time. So, after the hot flush, your engineer will need to dose the system with inhibitor. This ensures that sludge is constantly broken down into small particles.
They’ll then fit a magnetic system filter. These are designed to catch all the particles that the inhibitor has broken down.
Each year, you should have an annual boiler service. With this service, you’ll need to ask your boiler engineer to clean out the system filter.
Once these units are full, they won’t be able to catch anymore heating sludge, so ensuring the body of the filter is clear is important when it comes to protecting your heat exchanger.
What is limescale and how would that affect the heat exchanger
Limescale is similar in a way to heating sludge. But, rather than rust, limescale comes from minerals in water. Throughout the UK, there are soft, moderate and hard water areas. If you live in a “hard” water area, there’s a good chance that it’s limescale causing a problem with your boiler.
Limescale attaches itself to parts and once it does, it’s extremely hard to shift. Typically, where limescale attaches itself, that area will burn hotter. So, this could easily cause part of the heat exchanger to be burning too hot, overheating water in the process and leading to the 433 fault code being displayed, as well as a lock out.
But, the problem doesn’t stop there. Limescale on heat exchangers can lead to cracks, and once it’s cracked it will need replacing. Typically, a new heat exchanger is going to cost hundreds of pounds.
What can be done to remove limescale, and protect my Baxi boiler in the future
Rather than central heating inhibitor, a boiler engineer can use a limescale specific chemical. This will help remove the loose limescale throughout the heating system (not just on the heat exchanger). These limescale particles can then be removed via a hot flush.
Like central heating sludge, there is a specifically designed filter to catch limescale particles. You’ll need to ask your boiler engineer to fit what’s known as a limescale reducer (sometimes called in line scale inhibitors, or scale filters).
What does the NTC thermistor have to do with the 433 fault code on my Baxi boiler
The NTC thermistors on your boiler monitor temperatures on the flow (hot water leaving the boiler) and the return (water coming back to the boiler to be re-heated). Our focus here, is on the flow.
If there’s a sensing fault with the NTC thermistor on the flow side of the boiler, it might be giving the PCB incorrect resistance readings (in ohms). The PCB then converts these resistance readings into temperatures. If it’s over 95 degrees, the PCB will lock out the boiler.
To ensure that it’s not an NTC thermistor fault causing the boiler to lock out when it shouldn’t, your boiler engineer can run tests.
They can test for resistance and power on the thermistor using a multi-meter. And, if they find that the NTC thermistor is causing the fault, it can simply be replaced.
My boiler engineer thinks the heating pump is the cause of the 433 fault code, how can this be
Your boiler’s pump is responsible for circulating water around the heating system. So, if it’s restricted in any way, that circulation is going to be lower than it should be. And, when this is the case, water will stay in the heat exchanger for too long and overheat.
- Air locks
- Central heating sludge build-up
- Limescale
- Seized shaft and/or bearings
In around 1 hour, they’ll be able to remove any air locks, sludge, limescale and check that the pump works freely.
Once this is done, they’ll be able to check the speed setting on the pump. Most pumps have three different flow rates. Like a circulation restriction, a low speed setting will mean that the heat exchanger quickly gets over temperature.
If the pump on my boiler needs replacing, how much is it likely to cost
You want to be looking at pumps from top quality brands such as DAB and Grundfos. Typically, you should expect to pay around £250 for a pump replacement; that includes both parts and labour.
What does the PCB have to do with the 433 fault code on my Baxi boiler
Before replacing any parts, your boiler engineer will want to test the PCB. It’s the PCB that controls all electronic components in your boiler. It’s also the source of fault codes that are being displayed on the control panel.
The problem with this, is that the boiler is heavily reliant on the PCB. If the PCB was to malfunction, the boiler will work intermittently, and even when fault codes are being displayed, they could be incorrect.
Like the NTC thermistors, your boiler engineer will be able to test the PCB using a multi-meter. If there’s any sign of intermittent power, they’ll be able to check connections and wiring.
Something as simple as one loose connection could be enough to make the PCB malfunction. Re-securing this connection could be the quick and easy fix needed to clear the 433 fault code on your boiler.
If the PCB is at fault, how much is it going to cost to replace
The PCB is the most expensive part on your boiler. You should expect to pay around £500 for a replacement.
And with repair costs this high, you’ll want your emergency boiler engineer to check all other expensive components. If many of these are showing signs of excessive wear, the wise option would be a boiler replacement, rather than a repair.
Other Baxi boiler issues
For more boiler issues regarding the Baxi Boiler then please visit the Baxi Boiler Problems And Cures page.