Exactly,
If you couldn't set your unit properly with cold water first then you won't have a hope with hot water. Get your pressure callibration and flow settings perfect with cold first.
Now, when you use a heater, your hoses are going to expand, your controller will not cut the pump as soon as it used to therefore be prepared to drop the dead end pressure or watch your connectors blow apart. Your flow setting will probably remain the same.
You can't expect your controller settings to match everyone elses - every system is slightly different.
At the moment you simply have so much dead end pressure that the relief valve in the bottom of your heater is blowing to prevent damage.