- Boilers
- Gas boiler
H07
Junkers H07 boiler code: heating water pressure too low
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On the Junkers CerapurComfort ZWBE, H07 warns that heating water pressure is too low. Check the pressure gauge: normal is 1 to 1.5 bar. The manual asks for refilling to be done by a technician, who should also find out why pressure is dropping.
Safety first
Stop and check this first
- If you notice a smell of gas near the boiler showing H07, leave the gauge alone and avoid sparks, flames, switches or phones indoors. Turn the gas off at the meter, ventilate, leave the building and call the fire service and gas supplier from outside.
- Never refill above 2.5 bar: higher pressure opens the safety valve and water comes out again. The manual leaves refilling to a technician.
Safe checks you can perform
- Read the boiler pressure gauge
- Look for water under the boiler or at radiators
- Note when H07 appeared and whether radiators were bled
- Refill, bleed and pressure sensor test
Leave these tasks to a qualified professional
- Do not attempt this professional task: Refill and bleed the system
- Do not attempt this professional task: Find where the water is lost
- Do not attempt this professional task: Check the pressure sensor
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Refill and bleed the system
What they doThe technician restores water to the right operating pressure and bleeds the boiler and radiators, the first step the table gives for H07.
They must show youthe gauge inside the agreed range after bleeding.
In writingthe final pressure and the target pressure for your system.
Find where the water is lost
What they doThey trace where the circuit loses water before closing the low pressure message.
They must show youthe leak point or the test that rules out losses.
In writingthe leak location and the repair carried out.
Check the pressure sensor
What they doIf the gauge reads correctly and H07 stays, they compare the sensor reading with real pressure and replace the sensor if it does not respond, the table's second step.
They must show youthe sensor's pressure value side by side with the gauge.
In writingwhether the sensor was replaced and the result.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Read the boiler pressure gauge
- Who:
- you, looking at the appliance gauge, without turning any valve.
- How:
- note the needle reading with the heating cold; the user manual treats 1 to 1.5 bar as normal operating pressure.
- Result that matters:
- knowing whether the gauge confirms the low pressure that H07 reports.
- If confirmed:
- below 1 bar, ask the technician to refill and trace the water loss.
- If not confirmed:
- if the gauge shows normal pressure but H07 stays, tell the technician: it points to the sensor.
- Evidence to keep:
- photo of the gauge next to the display showing H07.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de instalación y manejo para el técnico (6720847000) · Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
Look for water under the boiler or at radiators
- Who:
- you, by eye, without taking anything apart.
- How:
- check the floor under the CerapurComfort, radiator valves and visible pipes for drips or fresh stains; never block the safety valve outlet, as the manual warns.
- Result that matters:
- spotting whether pressure falls because the circuit loses water somewhere.
- If confirmed:
- point the technician to any damp spot you found.
- If not confirmed:
- with no trace of water, say no leak is visible so they can search with their equipment.
- Evidence to keep:
- photos of any drop or stain near the appliance or radiators.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
Note when H07 appeared and whether radiators were bled
- Who:
- you, thinking back over work done at home in recent days.
- How:
- recall whether anyone bled radiators, drained a radiator or had seen the pressure drop before H07 came up.
- Result that matters:
- giving the technician clues about how much water is missing and since when.
- If confirmed:
- recent bleeding explains part of the drop; refilling is still the technician's job.
- If not confirmed:
- if nobody touched the system, the pressure loss needs a leak search.
- Evidence to keep:
- date of the message and list of recent radiator work.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
Refill, bleed and pressure sensor test
- Who:
- qualified heating engineer or Junkers authorised service.
- How:
- refill heating water through the filling device without exceeding 2.5 bar, bleed the appliance with its service function and compare the gauge pressure with the boiler's own reading.
- Result that matters:
- H07 clearing at the right pressure, with sensor and gauge agreeing.
- If confirmed:
- they record the best operating pressure for your system.
- If not confirmed:
- if the message stays with correct pressure, they test or replace the pressure sensor.
- Evidence to keep:
- job sheet with final pressure, cause of the loss and sensor condition.
The user manual asks for refilling to be done by a specialist; above 2.5 bar the safety valve opens.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de instalación y manejo para el técnico (6720847000) · Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Junkers
- Product type
- Gas boiler
Known code variants
- caldera Junkers H07
- Cerapur H07
- CerapurComfort H07
- H07 baja presión
- Junkers H07
- Junkers H7
What it means
The operating and fault message list for the CerapurComfort ZWBE 25-3 C and 30-3 C includes H07 with the display text Low pressure and the description water pressure too low. It gives two steps in order: top up water and bleed the system and, if that is not enough, replace the pressure sensor. The user manual puts normal operating pressure between 1 and 1.5 bar, asks you to agree the best pressure for your system with the technician and leaves refilling to a specialist. A fault in the sensor itself, defective or not connected, has its own code (H25).
Warnings and stop conditions
- Criticaleditorial warning
If you notice a smell of gas near the boiler showing H07, leave the gauge alone and avoid sparks, flames, switches or phones indoors. Turn the gas off at the meter, ventilate, leave the building and call the fire service and gas supplier from outside.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de instalación y manejo para el técnico (6720847000) · Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
- Mediumeditorial warning
Never refill above 2.5 bar: higher pressure opens the safety valve and water comes out again. The manual leaves refilling to a technician.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de instalación y manejo para el técnico (6720847000) · Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
Symptoms and causes
Probable causes · in order
- Heating circuit short of waterCommon
Junkers' first fix for H07 is to top up water and bleed the system. That means the circuit holds less water than it needs and may have air left after refilling.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de instalación y manejo para el técnico (6720847000) · Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de uso de la caldera mural a gas de condensación (6720847002)
- Faulty pressure sensorPossible
If H07 stays after topping up and bleeding, the table's second step is to replace the pressure sensor. Its reading may not match the real circuit pressure.
Evidence: Junkers CerapurComfort ZWBE 25-3 C y 30-3 C, instrucciones de instalación y manejo para el técnico (6720847000)
Virtual technician
Does H07 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Junkers (Bosch Termotecnia) · 2015 · manual
- 2
Junkers (Bosch Termotecnia) · 2015 · manual
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