Central Heating Header tank

[dme1]

I am helping bruv-in-law refurbish a bungalow. We have 7 days. Today we want to remove Rads from the (back boiler, pumped heatin/ gravity hot water) heating system. Can't find CH header tank or a cold feed into heating system. Maybe sealed system I thought, but where is the fill up point?
Started draining CH system and we found the Hot water header tank started filling up? Closer inspection found this was an open vent system with CH vent into domestic HW header tank! AND the cold feed to CH was via the domestic hot water circuit!! (presumeably pipes join under the floor). So we have a combined HW and CH header tank!
Hopefully the installer didnt put fernox in the tank!!

My questions are:
Was this standard practise in the old days? and is it dangerous/ unhealthy in any way??

 

[dme1]

blimey!

 

[AnonymousImport]

Sounds like you have a primatic hot water cylinder.

It has an internal air bubble for central heating expansion, and to keep central heating water separate from domestic hot water.

Although the two waters are separate, you should not have an inhibitor!

 

[MANDATE]

I agree with mrpym. I have a primatic HW cylinder and no header tank, installed about 1974 when house was built along with 11 others. The idea didn't last long and they are no longer produced. Cold water is fed to the base of the cylinder.