Zoning an old CH system... zone valve placement?

[garmcqui]

Hi all,

I'm planning a mild upgrade my parents old gravity fed (fully pumped) oil-fired central heating system over Easter. The current setup is rather strange - "non standard" shall we say? This is a rough mock-up of the current plumbing setup:



Notice there is no open vent pipe, just a combined cold feed and expansion pipe, which is attached on the positive side of the pump to the feed pipe to hot water cylinder! Not ideal, I think you'll agree.

Currently there is no control whatsoever, just "on/off". I'm planning on adding a Honeywell wireless programmable thermostat, changing all radiators to TRV's (except in the living room where the thermostat will be) and adding a couple of zone valves so DHW and CH can be turned on independently of one another (currently they are both on or both off). I will also put an automatic bypass valve in.

TRV'ing the rads is fine, as is setting up the thermostat etc. However, placement of zone valves is perplexing me. With the lack of vent, I understand I have to be careful not to isolate the feed/expansion if one or both of the valves are closed.

I had originally intended to place the zone valves here (indicated by yellow boxes):



However, in order to avoid isolating the feed/expansion pipe, perhaps I should site the DHW zone valve here instead:



Or would that still not work?

Any advice appreciated.

Thanks

 

[missplumb]

If the cold feed and vent is off the flow as shown then why not put your zone valves on the returns where they meet near the boiler, keeps all your control wiring in the same place and the vent pipe is always clear.

or go with plan b

 

[townfanjon]

You must have your cold feed / expansion tee first , before any zone valves pumps etc etc

 

[garmcqui]

If the cold feed and vent is off the flow as shown then why not put your zone valves on the returns where they meet near the boiler, keeps all your control wiring in the same place and the vent pipe is always clear.

or go with plan b

Thanks for replying.

Putting them on the return sounds like it could be a plan. 2 questions:

1. Currently, what's stopping the pump pumping water up the feed pipe into the f&e tank?

2. If zone valves were closed, and pump came on (almost impossible as zone valve end switches wil be controlling the pump and boiler), would the pump simply pump water up the feed/expansion pipe?

Thanks

 

[garmcqui]

You must have your cold feed / expansion tee first , before any zone valves pumps etc etc

I know, but I can't go changing the location of the cold feed now the boiler and pump are in a garage about 30m from main part of the house. The f&e tank is in the loft of main house.

 

[townfanjon]

Your feed / vent is your safety, if something goes wrong you, well just think !. You have virtually sealed the system without any expansion relief ,you potentially will get pump problems , sucking in , pumping over as well .

 

[garmcqui]

Ok. I see, cheers.

So if I did as suggested above, and put the zone valves on the returns into the boiler, that should avoid sealing off the feed/vent from the system?

To compensate for lack of open vent, could I put a pressure relief valve (similar to what my unvented cylinder has) somewhere in the system, perhaps in the garage near the boiler?

 

[tamz]

Thanks for replying.

Putting them on the return sounds like it could be a plan. 2 questions:

1. Currently, what's stopping the pump pumping water up the feed pipe into the f&e tank?

2. If zone valves were fitted, and pump came on (almost impossible as zone valve end switches wil be controlling the pump and boiler), would the pump simply pump water up the feed/expansion pipe?

Thanks

1. The 4 gallon or so of water sitting in the F&E. Thats why its been piped (or altered) that way.

2. Fit an auto bypass

 

[garmcqui]

Ok that makes sense.

So so this combined feed and vent system they have is legit? I expected to see a vent pipe looping over the c&w tank.

Also, ever since moving in, they've always had trouble with the utility room radiator (which is the first in the system) needing bled every week or so. Often it's as if the whole rad is filled with air. All other rads are fine. What about their current setup could be causing this? Would fitting an air separator help?