This problem could have several possibility's, one could be a bad or corroded ground on the satellite system, thus allowing external interference to get into the system, another could that one of the pumps is connected to same AC power leg that the TV/Humx is on, when the hot water system comes on there could be a high frequency surge on that AC power leg, what ever is controlling that system is causing this spike/surge.
One thing to look at is the boiler electric or gas fired? If electric is it on a single phase or both sides of the AC mains? (connected to both sides of the AC main) If dual phase connection then the following test may not be performed.
If it's electric and single phase then you need to see if it's on the same AC phase as the TV/Humax system, this would require an Volt meter to measure the AC voltage and a long extension cord, long enough to reach the location of the boiler.
You plug the extension cord into where the TV/Humax AC power surge protector is located, the other end of the extension cord is used to test the voltage at the boiler, if the voltage reads zero volts then you have a possible spike problem on that side of the AC, one way to possible eliminate this spike is you use some ferrite beads on the AC line at the boiler, this may require an electrician to do this job.
If you get a voltage reading then your TV/Humax system is on the other phase of the AC main supply, and the problem may be at the TV/Humax side.
Note: if you are not comfortable working with AC mains voltage then a electrician should be contacted to do the test.
If the tests prove out that the TV is on the same leg as the boiler then try find a AC socket that is on the other phase, us the extension cord and plug the TV/Humax system into this side of the phase, try the hot water, if the problem goes away you may need to run a cord to the other plug.
Sorry long winded too much coffee this morning.....
