There are a few scenarios that can lead to a lack of hot water. These include a faulty diverter valve (typical, if the heating works, but hot water doesn't). But, it could also be due to lack of power, a stuck Y/S-plan valve, faulty PCB unit, or even a problem with the heating pump.
Pressure issues: Over or under pressurisation With the likely culprit being the aforementioned leakage, under or over pressurisation could result in no hot water from your combi boiler. If your boiler is low on pressure, it can usually be solved simply through a DIY top up. It is going to be time to call in a Gas Safe Engineer!
