I would seriously consider turning it on at 0 degrees Celsius.
At least one degree above freezing?
I guess you are asking about daily air temperature. Once the surface has melted, the only concern is the above ground pipes freezing. If you leave the pump running all the time, the chance of freezing is very low.
Assuming you don't mean water heating systems, and just mean normal fresh (drinking) water systems, then they freeze at 0 degrees Centigrade like all water. But in the case of for example a home, the plumbing protected from freezing in a few different ways. Firstly most homes that are lived in have some form of heating, so this keeps the ambient temperature of the water in the pipes above freezing. Pipes that are in places more likely to be exposed to freezing, such as lofts, and roof cavities will be insulated with pipe lagging to protect them from freezing. Plus remember those pipes in roof cavities will benefit from heat rising from the home/building, helping to keep those pipes above freezing. If the subject of your question is in relation to 'burst' pipes caused by frozen water in the pipes expanding and literally tearing the pipes apart, then this will start to happen at about 20 Degrees Fahrenheit or -6 degrees Centigrade. Remember that a little freezing is not a major problem, as plumbers sometimes use special freezing kits, that will freeze a short section of pipe to block it off temporarily, while they work on the pipes.
There is no single best way to keep pipes from freezing. Insulating (wrapping) pipes is a common method. Leaving the cold water faucet open just enough for a slow drip is another method to prevent freezing.
If it is at freezing temperature, then you have an issue with uninsulated pipes.
When the temperature is 47 degrees, NOTHING is in danger of freezing !
If the outside air temperature is above about 30 degrees F, then yes; if the temperature is below that, then you should open the faucet to a slow trickle of water. If the water is moving, it probably won't freeze in the pipes and break them.
The minimum it can be set is 45 degrees F. You think the engineers would design it to allow pipes to freeze? Maybe they would if they did not do well in college.
You answered you own question: at freezing. At or near 32 degrees F your pump should be turned to keep water moving. moving water doesn't freeze. It is important that any exposed pipes, filter and pump have moving water at freezing as this water will freeze first and cause the item to crack. That's expensive as compared to the few cents it costs to operate the pump. Water starts to freeze at 32 degrees. So it best to turn pump on at approx. 35 degrees & leave on until the tempt. rises to 35
Pressure has nothing to do with pipes freezing. It is just exposure to cold.
Doesn't matter. the trick is to watch the weather and if below freezing let run a tiny trickle constantly unitl weather warms. As long as water not standing still, you don't have to worry about it.
Water freezes at 32 degrees Fahrenheit (which is 0 degrees Celsius). The factors which might change the temperature at which your pool pipes may freeze are: - other materials (such as salt) which are dissolved in the water - the rate of flow (if any) of the water through the pipes - the pipe diameter - the insulating properties of the pipes themselves - whether the pipes are buried underground Good luck with your pool!