When one runs and the other does not, it usually means the boiler itself is alive and the fault sits in how it shares its heat between your taps and your radiators. This guide walks through why you can have no hot water but heating works, and the reverse, along with the simple checks worth trying before you book anyone.
A combi boiler cannot do both jobs at once. Inside sits a diverter valve that sends the hot water either to your radiators or, the moment you open a tap, to a heat exchanger that warms the mains water for your taps and shower. Sensors tell the boiler when a tap is running so it can switch over.
Because that switching depends on a moving valve and a couple of sensors, a fault often shows up as one function working perfectly while the other does nothing, which is exactly the pattern that points to the diverter or its sensors.
If your radiators heat up but the taps stay cold, the usual suspects are:
The reverse, hot taps fine but cold radiators, tends to point to:
A few quick checks often save a call-out or at least speed one up:
If everything looks right and one function is still dead, the fault is inside the boiler.
A Gas Safe registered engineer can test the diverter valve, sensors and heat exchanger, free or replace a stuck valve, and descale or swap a blocked exchanger. These are common, well-understood repairs. Because they involve dismantling the sealed appliance, they are not DIY jobs. If you ever smell gas, stop, leave the property and ring the National Gas Emergency Service on 0800 111 999.
When heating and hot water disagree, the boiler is usually fine and the fault is in the valve or sensors that share its heat, which is good news because those are routine fixes. Run the quick checks first, then note any fault code. Omega Breakdown will diagnose which part is at fault and confirm a fixed price before any work, so you are not paying to guess.
Enter your error code or book a vetted Gas Safe engineer at a fixed price — no callout fee.