Heater cycles on and off, and takes for ever to finally heat.
If the ENGINE is taking a long time to reach normal operating temperature, you may need a new thermostat.
As far as heater cycling on and off, do you mean the blower motor?
When the heat is on , the boiler blows Ofer a while the stops, the starts to blow again, then stops. It continues to cycle on and off. I don’t think it is the thermostat, as I had the water pump and thermostat repaired about 7 months ago.
My guess is the blower Motor is starting to fail, when the fan motor gets hot, it shuts down, but that is just a guess.