gravity hw pumpeed htg boiler

[buckley plumb]

need a bit of advise on the following. boiler in basement floor standing 4 pipe gravity hw pumped htg. pump in basement by boiler .customer wants a new htg only boiler as pipework in concrete floors etc. the cylinder is on the 2nd floor and the f&e tank in the loft . the vent arrangement is the old way vent on the cyl feed at cylinder and feed on cyl rtn at cyl.the new boiler will be fitted in basement with a s plan .the problem being the feed and vent there is no way of getting another pipe from 2nd floor to basement . i know its not perfect but the only way i can think of is a combimed feed and vent on the cyl rtn . can anyone advise a better way

thanks ant

 

[diamondgas]

Do you not fancy sealing the system Ant? Otherwise, although not conventional, a combined f&v on the return will do the job you could pipe the cylinder coil; flow bottom return top to give any major overheat a relatively clear route to the expansion tank? 🙂

 

[ecowarm]

Agreed a sealed system would be good

 

[buckley plumb]

Do you not fancy sealing the system Ant? Otherwise, although not conventional, a combined f&v on the return will do the job you could pipe the cylinder coil; flow bottom return top to give any major overheat a relatively clear route to the expansion tank? 🙂

no chance of sealing it some of the pipes on show are green this house is old but just been fully decorated .i was thinking of an auto bypass but this would just be linking the boiler flow and rtn at boiler not realy doing the job of allowing the flow past the zone valves.i was thinking of putting the auto bypass after the pump on the flow then connecting back in on the flow after the zone valve to the hw to give a route if the boiler over heated but this would not give positive shut off for hw .if the boiler overheated with just a combined f&vent on the rtn would it be sufficient .

ant

 

[diamondgas]

The expansion pipe will do it's work as long as there are no valves to cut its route off. On modern design fully pump systems it doesn't make that much difference. Ring the manufactureres if your not sure Ant.

 

[Mike Jackson]

I've got over this in the past by converting to a low pressure sealed system. Retain the header tank but run a 22mm cold feed out of it. Fit a lever valve and single check valve before it connects to the system. Fit a large expansion vessel either in the airing cupboard or by the boiler. Fit a PRV by the boiler and you have a low pressure sealed system.

You may have to look at using a wireless cylinder stat if yo can't get wiring to the cylinder.

 

[diamondgas]

I'd guess your prv is set to a low blow-off pressure Mike yeh?

 

[Mike Jackson]

The lowest I've found is 1 bar which combined with an over size expansion vessel protects the system to a reasonable standard.

 

[diamondgas]

1 bar is still some 'head' of water though Mike ... 1000cm, 10m head! I picture the average domestic heating system half that 🙂 Still better than the 3Bar modern installs have to endure before they'll let loose!!! lol

 

[Nostrum]

Nice idea, never heard of this before. How do the manufacturers look at this idea? Only down side I can think of is that you have to go into the loft every time the pressure drops, which could be quite often on an old system with green pipes given the lack of 'excess' water in the system! Do you put a pressure gauge on down by the boiler?

 

[Dannypipe]

I've got over this in the past by converting to a low pressure sealed system. Retain the header tank but run a 22mm cold feed out of it. Fit a lever valve and single check valve before it connects to the system. Fit a large expansion vessel either in the airing cupboard or by the boiler. Fit a PRV by the boiler and you have a low pressure sealed system.

You may have to look at using a wireless cylinder stat if yo can't get wiring to the cylinder.

Never heard of this, but think its very clever idea.

Is it your idea or did you pick it up some where. Should be put in the plumbing tips section in my opinion.

 

[Mike Jackson]

It's an idea I adapted from some MIs that I've seen in the past with a top up bottle instead of a filling loop. You leave the lever valve open all of the time so it will top itself up if it loses any water. By using a large expansion vessel you are not putting the existing pipework under much extra pressure. I tend to put a pressure gauge down by the boiler but it barely needs it as the pressure is self regulating. You tend to need a few more AAVs on the system but with one on the coil it tends to be more or less self venting on the primaries.

 

[Nostrum]

Ok, i'm a little bit confused now!Maybe it's late and i'm not thinking straight, struggling to get my head round the logic of having an expansion vessel on a system with an F&E tank?

OP, can you use the existing feed and vent, coupled on to the existing gravity circ's to take your feed and vent straight back to the boiler, and in behind the pump at boiler? Then tee off from somewhere else on system for coil circs?


(edited as I think I read the question wrong, customer still wants cylinder!)

 

[Mike Jackson]

Don't think of it as an expansion tank, think of it as a top up bottle. I believe a lot of the original sealed systems were installed using this method.

 

[diamondgas]

Don't think of it as an expansion tank, think of it as a top up bottle. I believe a lot of the original sealed systems were installed using this method.

I vaguely remember coming across some cozywarm systems of the past similar with a none return valve fitted to the "manual" top up tank. Can't for the love of me remember an exp vessel or prv .. they must of had them though! Personally though, in the ops case, ok combining f&v. If the stats fail the expansion will still find its way up the return IMO 🙂

 

[buckley plumb]

Ok, i'm a little bit confused now!Maybe it's late and i'm not thinking straight, struggling to get my head round the logic of having an expansion vessel on a system with an F&E tank?

OP, can you use the existing feed and vent, coupled on to the existing gravity circ's to take your feed and vent straight back to the boiler, and in behind the pump at boiler? Then tee off from somewhere else on system for coil circs?


(edited as I think I read the question wrong, customer still wants cylinder!)

not possible cyl rtn would not be last tee due to rad pipes . another way i thought was to do a close couple f&vent on the rtn at the cylinder and but the pump on the boiler rtn thus the feed and vent is before th pump although it may be miles .but would it be ok pumping the rtn on a new boiler

 

[Nostrum]

How about using 1 of the gravity circs as a combined feed and vent back to the boiler, then taking a new flow for the coil off the heating and using the other gravity circ as a return from cylinder to prevent reverse circulation? Probably no different to previous but worth a thought if do able.

 

[diamondgas]

not possible cyl rtn would not be last tee due to rad pipes . another way i thought was to do a close couple f&vent on the rtn at the cylinder and but the pump on the boiler rtn thus the feed and vent is before th pump although it may be miles .but would it be ok pumping the rtn on a new boiler

Because you're combining the feed you will not have the same effect on the pipe as would seporate feed and vent pipes. I wouldn't advise fitting the pump on the return to be honest as you're adding restriction and isolation valves on a path that you'd prefer to have no restrictions what so ever yeh?