Zoning an older CH system - zone valve placement

[garmcqui]

Hi all, following on from this thread //www.diynot.com/diy/threads/no-boiler-bypass-needed.430470/, I thought I'd start a new topic as the subject has moved on from the boiler bypass.

I am intending to put a programmable thermostat and two zone valves into my parents aged (25+) CH system to enable them to control each independently. Currently if one is on, the other is on.

I have done a little investigating. It is a fully pumped open system, but it seems it has no open vent to the f&e tank in loft, just a cold feed pipe (which I presume also serves as an expansion pipe).

This is a rough outline of the current system:

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• garmcqui
• 25 Mar 2015
• 2

And this is where I propose to put the zone valves for CH and DHW:

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• garmcqui
• 25 Mar 2015
• 2

One thing you need to bear in mind is the change in the hydraulics to the system when the zone valves are inserted. The open vent and cold feed should not be interrupted by zone valves and you should design the new layout to remove the significant risk of 'pumping over' round the F&E tank.

My question is, based on what Simond advised above about making sure not to isolate the feed/vent, will this work? My worry is if the CH valve is open, but the DHW valve closed, the expansion/feed pipe is isolated.

Thanks

 

[stem]

A minor point, but your drawings are transposed.

You don't show the vent for the boiler F&E tank. If it has a combined vent and feed, then it's wrong because the Hot Water motorised valve is between the boiler and the vent. Contrary to previous advice:

when the zone valves are inserted. The open vent and cold feed should not be interrupted by zone valves

This is the sort of thing you should be looking to achieve, a clear unobstructed pipe from boiler to vent. The existing layout isn't ideal if the pump is in this pipe.

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• stem
• 25 Mar 2015
• 1

 

[garmcqui]

yes, that's what I said - there appears to be no seperate vent, just a cold feed pipe which I assume serves as an expansion pipe too?

So the DHW zone valve would need to be located closer to the hot water cylinder, AFTER the cold feed/expansion pipe has tee'd off?

 

[stem]

there appears to be no separate vent, just a cold feed pipe which I assume serves as an expansion pipe too?

A bit unusual, but can be done.

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• stem
• 25 Mar 2015
• 1

So the DHW zone valve would need to be located closer to the hot water cylinder, AFTER the cold feed/expansion pipe has tee'd off?

Yes. The idea is to have an unobstructed run of pipe between the boiler and the vent.

 

[Agile]

You don't seem to be realising that a system is potentially dangerous with no vent pipe!

Its a safety feature!

Both for inhabitants and the boiler.

Tony

 

[garmcqui]

Stem - that looks like it, but there's no air seperator, just a normal T-junction.

Tony I do realise the vent is a safety feature, hence the exclamation marks in my original post. However, it's functioned ok like this for 25 years.

There is a 22mm cold feed/expansion pipe. Am I right in thinking that the vent would only be needed for expansion/pressure relief if, somehow, this pipe became blocked?

 

[Agile]

No, you obviously don't understand the way a vent pipe works!

The air bag in my car has potentially functioned OK for the last 25 years.

But I just want it to work in the future in case I have a serious accident!

Tony

 

[garmcqui]

ok, could you explain how it does work then?

Why does the diagram stem linked to say it is possible?