The house that we moved into has a Rayburn Regent oil fired cooker/water heater in the kitchen. When I had it serviced I was informed that it was originally a solid fuel burner which had been converted.
The water that it heats is stored in an emersion heater tank in the loft and the water is scorching hot. No need to switch on the emersion at all usually.
A small central heating system was also added by the previous owners (6 small radiators) but all that happens when the pump is switched on is that the hot water disappears from the emersion, one or two of the radiators become very luke warm and that is it.
I have tried leaving it on for hours but it just stays like that. I have also tried just leaving one radiator on but nothing improves the situation.

The water that it heats is stored in an emersion heater tank in the loft and the water is scorching hot. No need to switch on the emersion at all usually.
A small central heating system was also added by the previous owners (6 small radiators) but all that happens when the pump is switched on is that the hot water disappears from the emersion, one or two of the radiators become very luke warm and that is it.
I have tried leaving it on for hours but it just stays like that. I have also tried just leaving one radiator on but nothing improves the situation.