Error DLQ 33 in reality most often indicates a lack of signal about the presence of flue gas pressure or a malfunction of the sensor itself pressure switch in gas boilers of the Baxi and De Dietrich series. This combination of symbols on the display means that the electronic control board does not receive confirmation that the chimney draft is sufficient for safe combustion. The unit is blocked instantly to prevent carbon monoxide from entering the room, so this code cannot be ignored.
The appearance of the DLQ 33 code is often accompanied by a characteristic cycle: the boiler tries to start the fan, makes several unsuccessful ignition attempts, and then goes into lockout mode with a flashing indicator. In some cases, the user may hear the hum of the turbine, but the flame never ignites. Understanding what is behind this code allows you to quickly determine whether you need to call a technician or whether the problem can be solved yourself by checking simple parameters of the smoke removal system.
The operation of modern gas boilers is based on constant draft control, for which the pneumatic relay or differential pressure sensor. When you start the heater, the control board first sends a command to turn on the exhaust fan. If the turbine reaches the required speed, a vacuum is created in the combustion chamber, which is recorded by a sensor. It is this signal that confirms that combustion products will be discharged outside and not into the apartment.
Code DLQ 33 signals a break in this logical chain. The board “sees” that the fan is spinning (or should be spinning), but the pressure sensor is silent. This may occur due to mechanical sticking of the relay membrane, broken wires, or simple icing of the pipe head on the roof. It is important to understand that the boiler electronics do not distinguish the reason - for it there is only the fact of the absence of a signal, which leads to an emergency stop.
There is a misconception that error DLQ 33 is always associated with the breakdown of expensive electronics. In practice, the physics of the processes is often to blame: a strong wind that has covered the pipe with snow, or condensate that has gotten into the sensor tube. In such cases, replacement of equipment is not required; it is enough to eliminate external factors. However, if the problem lies in the pressure switch, its characteristics may have changed due to wear of the rubber membrane.
⚠️ Attention: Never try to forcefully close the pressure switch contacts to start the boiler. This disables the safety system, which may result in carbon monoxide poisoning or a gas explosion in the combustion chamber.
The main reasons for the appearance of error DLQ 33
When understanding the reason for the appearance of code DLQ 33, it is necessary to take into account the design features of your boiler model. In most cases, the problem lies in one of three main areas: the smoke removal system, the pressure sensor itself, or the electrical circuit. The fan may work properly, but if the gas path is blocked, the pressure will not change and the sensor will not work. A common cause is the formation of an ice plug in a coaxial pipe in winter.
Another common scenario is a leak in the air tube connecting the combustion chamber to the sensor. If condensation has formed in the tube or it is kinked, the pressure signal will not reach the membrane. In models Baxi Eco Four or De Dietrich the tube may be positioned so that condensation flows into it if installed incorrectly. It is also worth checking the integrity of the wires going to the relay terminals, since vibration during boiler operation sometimes leads to their burning out.
The condition of the fan itself deserves special attention. If the turbine bearings are worn out, it may not develop the necessary speed to create the required vacuum. In this case, the mechanical part of the system is functional, but the performance of the node has fallen below a critical threshold. The control board records this as a traction error and issues code DLQ 33, although technically the fan is humming and rotating.
- ❄️ Icing or snow drifting on the outer chimney head, blocking the exit of gases.
- 💧 Condensate gets into the pneumatic tube or pressostat chamber, blocking the movement of the membrane.
- 🔌 Oxidation of contacts or broken wires in the pressure sensor connection circuit.
- ⚙️ Wear of fan bearings, which does not allow creating the necessary vacuum.
Diagnostics of the smoke removal system and fan
The first step in troubleshooting should be visual and acoustic diagnostics. When trying to start the boiler, listen carefully to the sounds it makes. If you hear the fan hum, but after a few seconds the relay clicks and an error follows, it means that the turbine is working, but there is not enough thrust. If there is silence or only a quiet hum is heard without an increase in speed, the problem may be in the fan itself or the control board.
Be sure to check the condition of the coaxial chimney. In winter, an “icicle” of frozen condensate often forms at the end of the pipe, which completely blocks the channel. This is the most common, but common reason for the appearance of DLQ 33. It is enough to break the ice for the system to work. Also make sure that there is enough fresh combustion air entering the room, especially if the boiler is installed in a sealed room.
In case of strong wind, backdraft or flameout may occur in the chimney. If error DLQ 33 appears only in windy weather, install a deflector or wind vane on the head of the pipe.
For a more in-depth diagnosis, you will need to remove the boiler casing and inspect the pneumatic tube. It is a thin silicone hose that runs from the combustion chamber to the sensor. Remove it and blow it out. If there is water inside, it must be removed. Check the connections for cracks. Sometimes the hose itself dries out and bursts, which is why the vacuum is not detected.
⚠️ Attention: Before removing the boiler casing, be sure to turn off the gas tap. Work inside gas equipment may only be carried out by qualified specialists; independent intervention may violate the warranty.
Checking and replacing the pressure switch
If external factors are excluded, the next candidate for verification is yourself. pressure switch. This is a mechanical device with a membrane and electrical contacts. Over time, the membrane may lose elasticity or become deformed, and the contacts may oxidize. You can check its performance with a multimeter in dial mode. In the initial state (without vacuum), the contacts should be open or closed depending on the model (normally open or normally closed).
When applying vacuum (if you can create it artificially, for example, with your mouth, being careful), the contacts should change their state with a characteristic click. If there is no click, or the contact does not appear/disappear, the sensor is faulty. In boilers Baxi Sensors with an adjustable response threshold are often used, but in domestic conditions their adjustment is not recommended due to the risk of a safety violation.
☑️ Checklist for checking the pressure switch
Replacing a pressure switch is not a complicated procedure, but it requires precision. It is necessary to select an analogue with exactly the same response pressure parameters (indicated in Pascals on the body). Installing a sensor with other parameters will lead either to constant errors or to the boiler operating without proper draft. After replacement, be sure to check the tightness of all connections.
Electrical circuit and control board
In rare cases, error DLQ 33 may indicate problems with the electronic board itself. If the fan is working properly, the pressure switch is new and working, and the wires are intact, the fan control triac may have burned out or the input circuit of the board responsible for reading the signal from the sensor has failed. Board diagnostics require professional knowledge and equipment.
Users often confuse a sensor error with a power problem. Power surges in the network can lead to malfunctions of the board, causing it to incorrectly read sensor readings. Installing a voltage stabilizer can solve the problem if it is caused by external factors. It is also worth checking the boiler's grounding, as static electricity can affect the operation of sensitive electronics.
| Component | Problem Symptom | Test method | Solution |
|---|---|---|---|
| Pressostat | No click, no resistance change | Testing with a multimeter | Replacing the sensor |
| Fan | It hums, but doesn't gain any momentum. | Visually and auditorily | Cleaning or replacement |
| Pneumatic tube | Condensation, kinks | Visual inspection | Purge, replacement |
| Control board | No power to fan | Output voltage measurement | Board repair or replacement |
Technical parameters of a typical pressure switch
Typically, such sensors operate at a vacuum of 40 to 60 Pa. The body is often marked with, for example, 45/30 Pa. This means that when a vacuum reaches 45 Pa, the contacts close and open when it drops to 30 Pa. Using a sensor with other parameters is unacceptable.
Seasonal factors and prevention
Owners of private houses often encounter error DLQ 33 during severe frosts. This is due to the physics of the release of wet combustion products into the cold. The condensate freezes faster than it can drain, forming ice stalactites at the outlet of the pipe. Prevention involves correct installation of the chimney with a slope towards the boiler (to collect condensate in a container) and the use of insulated pipes.
Regular maintenance can avoid most problems. Cleaning the combustion chamber, checking the condition of the heat exchanger and purging the pneumatic system should be carried out at least once a year. This is especially true for gas boilers operating in intensive mode. Ignoring prevention leads to the accumulation of soot, which can also clog the pressure tap holes.
Main conclusion: In 80% of cases, error DLQ 33 is solved by checking the chimney for icing and purging the pneumatic tube from condensate, and not by replacing the electronics.
When you need to call a specialist
Despite the possibility of self-diagnosis of some components, there are situations when the intervention of a service technician is mandatory. If you have checked all external factors, purged the tubes, and made sure the wires are intact, but error DLQ 33 persists, the problem is deeper. This may be a hidden board defect or the need for complex adjustment of the gas valve.
A specialist is also needed if major components, such as the fan or the control board itself, need to be replaced. This work involves disassembling the gas part of the boiler and subsequent pressure testing for leaks. Violation of the tightness of gas paths is deadly, therefore, after any intervention in the gas path, a check with a soap solution or a gas analyzer is required.
Is it possible to ignore error DLQ 33 and continue to operate the boiler?
No, you can't. An error means that the safety system does not confirm the presence of traction. Operating a boiler with a blocked smoke exhaust system will lead to the accumulation of carbon monoxide (CO) in the room, which is fatal to people.
Why does the error only appear in windy weather?
A strong wind can blow into the pipe, creating excess pressure or, conversely, disrupt the flame and disrupt the stability of the draft. The sensor detects instability of parameters and blocks operation. The solution is to install a deflector.
How often should the pressure switch be changed?
The pressure switch does not have a strict time schedule for replacement. It changes only in the event of a malfunction. Under normal operating conditions and high-quality gas, it can last 10 years or more.
Does gas quality affect the appearance of DLQ 33?
Indirectly affects. If the gas has low pressure or incorrect composition, the combustion process may be unstable, which affects the parameters of the flue gases. However, the DLQ 33 code itself still indicates a problem with traction, and not with the composition of the gas.