The Biasi Activ A Plus is a mains gas combi / regular boiler. Below are the faults it most often develops, what the error codes mean, and how to get it fixed at a fixed price by a Gas Safe registered engineer.
Variants covered: 16S, 25S, 30C, 35C
Hot taps run cold while heating still works — commonly the diverter valve, the flow sensor or the plate heat exchanger scaling up.
The gauge drops below ~1 bar and the boiler cuts out — usually a small leak, a tired expansion vessel or a weeping pressure-relief valve.
It tries to light, fails and locks out — often the spark electrode, gas valve or a flame-sensing fault.
Drips or staining under the case — a seal, the pump, the heat exchanger or a corroded pipe.
Rumbling on the heat exchanger, usually limescale or sludge restricting flow.
Cool rads or slow warm-up — often the pump, a sticking motorised valve or air in the system.
These are the likely causes — a Gas Safe registered engineer confirms the fault on site before any work. If you can smell gas, stop and ring 0800 111 999.
Read it out or type it into our boiler fault-code checker and we'll tell you what it means and what the repair costs.
One fixed price, no callout fee, a vetted Gas Safe engineer who covers your postcode.