As it started through the rinse cycle, it stopped and flashed error codes (H and F I believe). The door locked button is lit and I've tried all the normal suggested ways to get the door unlocked, to no avail.

Many modern washing machines display error codes if they detect a fault, but not all washing machines display a readable error code, some indicate an error by flashing, or lighting some of the lights.

Hotpoint, Indesit, Zanussi error codes

Hotpoint, Indesit washing machines and Zanussi washing machines are some common appliances that display coded error codes. On their more expensive models, they display readable error codes but basic models (without digital displays) use flashing lights to convey the error fault code.

If your washing machine malfunctions and you can see some of the lights flashing, or one or more option lights have lit up, then make a note of which lights are flashing and which option lights are lit. NOTE: the error code list engineers have only shows the option lights by number and not by name. Therefore you need to report the lights as LED 1 and 3, or 2 and 4 etc. and NOT "delay timer" and "extra rinse". Count the lights from the left (or from the top if in a column) and report as "led 1 and 3" etc.

No Option lights?

With basic washing machines that have no option indicator lights, count the number of flashes. For example, the door locked indicator may flash 7 times, pause, and flash another 7 times in a constant cycle which would indicate error code 7.

This information is vital, and needs mentioning when reporting a fault.