Drain cock for central heating

[John74813]

Hello, moved into a house that the previous owners lived in since new in 2006. I’d like to clean chemically clean, drain, and refill the heating loop. However, am unable to locate any drain cock on any radiators.

I have though located three pipes with cocks on in the garage (which is actually built under the house and therefore would be lowest point in the system).

Could one (or two?) of these be connected to flow and return? How would I find out - just try turning them? Why would there be three of them though?


I also have two under the boiler itself but wouldn’t make sense to drain from here (if they are for draining) as there is a radiator a floor lower than the boiler

Thanks in advance

 

[terryplumb]

Open each ,one at a time ,to establish what's draining. One may be for domestic water,and 2 for heating.

 

[Harry Bloomfield]

I also have two under the boiler itself but wouldn’t make sense to drain from here (if they are for draining) as there is a radiator a floor lower than the boiler

Are the drains lower than the lowest radiator?

If they are, they will syphon to a large extent, from that lowest rad.

 

[John74813]

the bottoms of the three drains pictured are probably in line with the lowest radiator in the house. The drains on the boiler are higher than half of the radiators

 

[John74813]

Spoke to some neighbours who have the same thing. They tell me one is for the upstairs rads, one for the downstairs rads, and one for the hot water system (presumably the red one)

Why would I need to drain the hot water system? It’s a combi boiler with no tank - what would there be to drain?

 

[Madrab]

Why would I need to drain the hot water system

legacy, if no more cylinder then it's probably redundant unless it's still connected and will drain the pipework.