About Us:
My name's craig Johnson, iv been plumbing for around 13 years now on everything from repair Jobs bathroom fitting, new builds right up to working on hospitals care homes, colleges, sports stadiums (Fulham FC oval cricket stadium)
On the way iv learnt how to tile, had a stint if fitting bathrooms for BBQ, fittings bathrooms on the side, tiling kitchens etc.
Answers:
Pressurised systems work on pressure, so even if your heatings turned off, if it drops pressure you loose hot water and heating, so you've either got a leak on your heating system or a problem with your expansion vessel.
Because the pump is operating at a higher speed when turned up
You may be better with the shower etc connections further away from the toilet waste as the amount of water running through it when the toilets flushed may pull water from your shower trap, another thing to check is if your 4" drainage pipe has a durgo on it at the highest point, a birdcage or a tile vent. because a property has to have a certain percentage of drainage pipes go to atmosphere to stop this problem