CH system draining confusion??

[mandlebrot]

I wanted to add a few rads to my system so after shutting off both sides of all rads and cold water supply I drained the system using a drain valve from downstairs. Anyway to cut a long story short it took ages to drain with what seemed like way to much water, after it finished I went to wash my hands and low and behold I had no hot water in the tank. Now I'm really confused as to why the domestic hot water tank should have emptied when I was draining my gravity fed CH using a drain valve off a rad. Can anyone enlighten me as to why this should happen and does it mean (not getting any sludge through my domestic hot water so doubt its mixing) that somehow my CH water is mixing with my domestic supply?

Steve

 

[ChrisR]

Sounds like you know the answer! Your heating coil in the HW cylinder is letting water pass through. If the water level in the loft CW cistern is above the level in the CH cistern, you wouldn't get water flowing the other way.

If you don't have a CH cistern, you have PRIMATIC cylinder, so you can drain the lot from the CH. Do a search and you'll see how they work

 

[mandlebrot]

Thanks for the info, I know I've got a header tank on top of the cylinder but having just recently moved in I really haven't yet been in the loft but will go up there tomorrow to check if I've got a CH cistern.

 

[mandlebrot]

I've now checked it out and it does indeed seem that I have a PRIMATIC system and maybe will think about changing the cylinder to the coil type once I've got the money and time to install the cylinder and header tanks. Thanks again for the info

 

[HarrogateGas]

Make sure you DO NOT add any inhibitr to your system.