sounds like you need to replace the heater core (pretty large job) or at least time consuming...good luck
You have a short in the cluster.
Low coolant? Bad thermostat? Heater core plugged,restricted or airbound? Heater control cable or valve not working?
If the temperature gauge is reading below normal operating temp after driving a little while it may be that your thermostat is stuck open. I replaced my thermostat and it fixed mine.
control fuse blows when you plug thermostat to base controlling a gas pack unit
The heater valve may not be engaging or the heater core may be blocked.
That is normal, It is a thermostat
My guess is the head gasket, have same problem. Nightmare
Bad Thermostat
Low coolant? Wrong thermostat temperature range? Heater core plugged,restricted or airbound? Water pump not circulating coolant? Temperature control cable not adjusted properly?
Thermostat is bad
COULD BE A BAD HEATER CORE COULD BE A BAD HEATER CORE sounds like the heater control switch needs replacing.if that doesnt fix it, you need new heater core
The heater core is plugged. Blow it out with a compressor. If that does not work replace the heater core.