Insulin on board

You get insulin stacking when you use insulin within the time it takes for the last insulin you took to be fully used by you, not about how many times you change your site.
So if the time is set on your pump to 4 hours for insulin (I believe many are set to 4 hours and this woulda been set up when you got your pump) then you will get stacking if you inject again in less than 4 hours from when you last did.

Or did you mean your insulin is just taking longer to be fully used?

@steveo4 there's a whole host of reasons.
You could be under cooking basal and topping up with bolus, lots of us do this when basal's need to change before we are aware.
You could be under cooking bolus's for meals.
Your rate of insulin action could have gone down, we have been in various forms of lockdown / reduced activity for some time and lower levels of activity / higher weights can cause insulin needs to increase.
There may be others but perhaps your only just taking time to look at IOB or even work it out and its always been like this.

If your controlling well then I would not worry too much TBH.

Hi @steveo4 I agree with Chas insulin stacking isn’t an issue if your control is ok, it’s when you’re levels are falling out of range that you need to look at the whole picture and start again with basal testing and go back to basics.

I don't understand what is meant by changing pumps sites affecting insulin stacking up.
In my experience, pumps report insulin on board based on bolus it has dosed and the iob time (how long insulin remains active in your body) configured on the pump.
It has absolutely no knowledge of the absorption rates at your pump site.