BoilerFaultCodesTechnical description
No primary temperature increase detected
What causes this fault?
This fault occurs when the boiler fires up but the sensors do not detect a sufficient rise in water temperature, causing the system to shut down for safety. The most common reason is that the water isn't moving through the unit properly, often due to a failed internal pump or a blockage in the pipework. It can also signify that the sensors responsible for measuring heat are faulty or that the main heat exchanger is clogged with debris.
This issue often surfaces during the first few cold days of autumn when heating systems are turned back on after being idle all summer, which can cause internal pumps to seize.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.