Glow Worm 38cxi slow startup

[Kevin Hartle]

Our Glow Worm 38cxi boiler is about 15 years old. When turning on the central heating in the morning, the boiler fires for a moment and the pump starts, then the green light goes off but the pump continues to circulate the water. The temperature of the water on the boilers digital display drops down to room temperature. After about 4 minutes from turning the boiler on, it ignites again and the boiler works normally. Is this 4 minute delay normal? Is there anything that can be done so that the boiler fires up immediately on startup? If we turn on a hot water tap the boiler fires immediately.