Hot water problem

[Clarebear123]

So if we put our hot water to come on at the same time as our heating or the hot water to start up after the heatngs been on a little while, the hot water seems to cut the heating off and just heat the water.

How do I stop this happening and get them both on together, it never used to do this??

[Cburns73]

Nest learning thermostat. Worked all winter with the red wire in the RH. We had a jumper to the RC on our old thermostat. Switch to cooling and our fan turns off freezing the ac line. Electrician came out and says it's the thermostat. When he uses a jumper to the unit down stairs it runs. Nest won't replace so trying to trouble shoot to see if I set it up wrong. I put the red wire in the RH and set my app with R not RH or RC as that's what Google stated to do. Did I do it right? I'm just trying to keep the fan on when our AC is on. It turns off within mins of kicking on.