Help me understand my C/H system a little more

[Topefisher]

First post, so be gentle please.

System: 19 yr old Open vented fully pumped with mid position diverter valve.
Boiler: Potterton Flamingo
3 port valve
3 speed pump
6 radiators
Installation is in a bungallow with most pipework dropping from the attic.
Boiler location: Garage

Each time I have had to drain the system for whatever the reason at the time ( Replacing leaking valves mainly) it has been a hell of a job purging the air from the system.

As a consequence I now use mains pressure to flush through and bleed the system.

To do this I have fitted a gate valve either side of the cistern feed to isolate the cistern.
To the outer sides of each gate valve I have fitted an in-line tap.

To the tap on the pump side of the feed, I open it and put in the mains water (protect/anti syphon type tap and hose connection so as not to contaminate water).
To the tap on the other side I connect a hose and open out to the drains.

I shut all the radiators down then opening and purging one at a time. The circuit through the water cylinder I treat a another radiator using its gate valve to shut off as required. This eventually purges all the air with just a tad left to vent from the radiator bleed valves themselves.

What I cannot undertstand is that I can only seem to do this in ONE direction. It flows from the boiler towards the pump and it will not flow in the opposite direction.

I have have read the information at the top of the forum and at one point it suggests that there may be some type of Anti-gravity or check valve in the system.

My questions are really just to gain a better understanding of what is happening and which are as follows:

1) Is it normal for the system to flow in one direction only, or do I have a fault?
2) If it does only flow one way, will there be a check/one way valve?
3) If there is a such a valve where would this likely be located?
4) The info at the top of the forum suggest that when I use this method for a system flush that it may be advisable to flush in both directions. Is this considered necessary?
5) If considered necessary how do you bypass the one-way valve?

Malc

 

[cowley]

Your type of system is one of the hardest types to purge of air, each drop to radiators should have a draw off fitted at low level preferably on both flow and return pipes draw offs on flow and return to boiler, air vents at all high points on all pipes in loft area.
When draining system drain all legs and radiators refill slowly venting from lowest point up, you should not have any type of valve in either the feed/expansion pipe or the open vent pipe, if you forgot to turn them back on after you fill the way you say you do you will be leaving your system in a dangerous condition, i don't think you would have a non return valve in the system you describe.

 

[Topefisher]

Your type of system is one of the hardest types to purge of air,
you should not have any type of valve in either the feed/expansion pipe or the open vent pipe, if you forgot to turn them back on after you fill the way you say you do you will be leaving your system in a dangerous condition,

Thanks for your reply.

Yes, my service engineer said that about my type of system.

The valves are not actually in the cistern feed or the vent pipe. They are in the main run from the boiler thru' to the pump. One positioned either side of where the feed enters it. Similar to the valves positioned either side of the pump for service/repair.

And yes I do have to take much extra care to ensure gate valves are open and taps are closed prior to system back on.

The rest of the system is as you mention except there is only one draw off at each radiator and one set of manual vents in the loft.

 

[kevplumb]

put a vent on each drop will save you some greif

 

[MANDATE]

Use lever to hold 3 port valve in mid position when refilling

 

[Topefisher]

put a vent on each drop will save you some greif

Kev,

Do you mean at the top of each drop but on the horizontal runs in the attic?
Do you mean on both sides i.e. feed and return?

Regards - Malc

 

[Topefisher]

Use lever to hold 3 port valve in mid position when refilling

Yes - Thank you. I have actually done this in the past.

 

[kevplumb]

put a vent on each drop will save you some greif

Kev,

Do you mean at the top of each drop but on the horizontal runs in the attic?
Do you mean on both sides i.e. feed and return?

Regards - Malc

assuming the pipework is level as close to the drop as you can get and both sides wouldn't hurt