Boiler upgrade, will the feed & vent posistion pump over?

[gassafe]

Hello guys & gals,


I am quoting a floor standing boiler replacement, the heating is pumped with cylinder on gravity flow & return with the usual 22 vent on flow & 15 cold feed into return (on cylinder).

All the flow & returns go back to the boiler, but when i fit a wall mounted regular boiler with pumped Y plan system, im just wondering wether I would have "pumping over" issues, there no way of getting the vent & feed before the pump like an ideal system design, and customer does not want a sealed system either. (pipes in concrete floor!)

Is there a way a re-arranging the cold feed & vent in airing cupboard so its okay, or would it not pump over anyway?...

Any advice appreciated, I am used to upgrading to sealed sytems than modifying tank fed!

 

[southcoastboile]

combined cf and ov in 22mm?

 

[gassafe]

combined cf and ov in 22mm?

I have heard about the combined cold feed & open vent trick, would that be best on the cylinder return or flow?

I only ask because the feed & vent would still be after the pump, so under posistive pressure on the flow side...

 

[Roger Welton]

I prefer to put the pump and control valves in the airing cubard, then pick up the heating flow and returns nearby (hopefully!)

 

[tamz]

You would be better with an S plan. Pump and valves on the return and combine feed and vent.

 

[JCplumb]

Turn the pump round?

 

[gassafe]

Turn the pump round?

Would this not upset the boilers electronic control... with the return temperature rising above the flow temperature?

 

[tamz]

Turn the pump round?

You don't want to do that.

 

[gassafe]

Worst case scenario if it pumped over on a sully pumped system could i add a sealded system kit but keep the system pressure lower? for example fill the system, vent rads, but not pressurise to 1 bar? The boiler would not cut out because it would be a regular boiler, and it would keep the pressure a bit lower. The system would still be full of water tho.

Would this be practical?

 

[Mike Jackson]

You need to check withe the MIs and see what they say before you start combining feeds and vents or putting pumps on the return. If they don't approve the method and something goes wrong with the boiler they may well refuse to honour the warranty until the system is piped to their liking.

Assuming that the heating flow and return are by the Boiler at the moment you're going to need to get at least one other pipe to the airing cupboard. You can then use one of the gravities as a primary flow, one as cylinder return and run a new Heating flow back down from the airing cupboard.

If this isn't feasible think about converting it to a low pressure sealed system. Fit a PRV adjacent to the boiler and an expansion vessel on the return in the airing cupboard. Instead of a filling loop fit a single check valve and isolating valve to the cold feed and do away with the open vent. If you oversize the expansion vessel there will be very little increase in pressure as the system heats up and you can fit a lower rated PRV to prevent the old system getting over pressurised in case of malfunction.


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[gassafe]

You need to check withe the MIs and see what they say before you start combining feeds and vents or putting pumps on the return. If they don't approve the method and something goes wrong with the boiler they may well refuse to honour the warranty until the system is piped to their liking.

Assuming that the heating flow and return are by the Boiler at the moment you're going to need to get at least one other pipe to the airing cupboard. You can then use one of the gravities as a primary flow, one as cylinder return and run a new Heating flow back down from the airing cupboard.

If this isn't feasible think about converting it to a low pressure sealed system. Fit a PRV adjacent to the boiler and an expansion vessel on the return in the airing cupboard. Instead of a filling loop fit a single check valve and isolating valve to the cold feed and do away with the open vent. If you oversize the expansion vessel there will be very little increase in pressure as the system heats up and you can fit a lower rated PRV to prevent the old system getting over pressurised in case of malfunction.


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Thanks for the advice MJ, the airing cupboard is a long way from the boiler with all pipework boxed in so thats not really an option.

I like the low pressure sealed system idea, and did not know there was such a named thing! What sort of PRV would you recommend with this? Im guessing a expansion vessel in the airing cupboard with the PRV placed on the boiler return would be okay because its all on the same pipe run with no valves etc.

 

[JCplumb]

Would this not upset the boilers electronic control... with the return temperature rising above the flow temperature?

oh yeah...
Well in my defence I am very very hungover and the old brain isn't on top form yet :sick:

 

[Mike Jackson]

Thanks for the advice MJ, the airing cupboard is a long way from the boiler with all pipework boxed in so thats not really an option.

I like the low pressure sealed system idea, and did not know there was such a named thing! What sort of PRV would you recommend with this? Im guessing a expansion vessel in the airing cupboard with the PRV placed on the boiler return would be okay because its all on the same pipe run with no valves etc.

I'm not sure if it's a named thing but it's a method that I've used several times over the years, quite often in rectifying a system where someone has converted a gravity system incorrectly. It's a variation on the original sealed systems that used to take there water from the cold down service to the hot water cylinder. By using the header tank as a dedicated feed you solve the issues that arise from needing to put a double check valve on a low pressure supply. Last one I did I used a 22mm single check valve on a 15mm cold feed to make the system fill easier. I managed to find a PRV as low as 1 bar which is still more than the system will have been under previously but a lot less than the 3 bar standard.

 

[gassafe]

I'm not sure if it's a named thing but it's a method that I've used several times over the years, quite often in rectifying a system where someone has converted a gravity system incorrectly. It's a variation on the original sealed systems that used to take there water from the cold down service to the hot water cylinder. By using the header tank as a dedicated feed you solve the issues that arise from needing to put a double check valve on a low pressure supply. Last one I did I used a 22mm single check valve on a 15mm cold feed to make the system fill easier. I managed to find a PRV as low as 1 bar which is still more than the system will have been under previously but a lot less than the 3 bar standard.

Ah, I thought you meant to remove the exisitng header tank.

So whats the difference between using mains to fill the system with pressure gauge & leaving it low pressure.

Does your design use a pressure gauge still, and has anyone else done it this way before?

 

[gassafe]

I have found 1 & 1.5 bar PRV that would probarly be adequate, would the expansion relief pressure need altering also?

 

[Mike Jackson]

Do you mean the expansion vessel pressure? As long as you oversize it then that can be lowered as well to .2 bar above system head.

 

[gassafe]

Do you mean the expansion vessel pressure? As long as you oversize it then that can be lowered as well to .2 bar above system head.

Yes, sorry i meant expansion vessel pre charge. I suppose a pressure gauge could still be fitted to be on the safe side.

Did you notice any problems re-filling the system? Does the single check valve cause problems trying to fill rads or vent radiators, or is the pressure from a tank fed system enough to open the valve?

 

[Mike Jackson]

I've not had any problems, you just need to make sure that you've got an AAV on the cylinder flow. I tend to put a pressure gauge on as it gives an indication of any problems with the pressure vessel.


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[John The Rad]

I would stick to a Y plan but connect the expansion pipe to the cold feed.
This will act as a by-pass and, as long as the connection is high in the airing cupboard then it will not be able to pump over, it will just return from the expansion pipe through the "by pass" and back into the system. (round and round).
If it is not trying to pump over then there's no harm done.

 

[gassafe]

I would stick to a Y plan but connect the expansion pipe to the cold feed.
This will act as a by-pass and, as long as the connection is high in the airing cupboard then it will not be able to pump over, it will just return from the expansion pipe through the "by pass" and back into the system. (round and round).
If it is not trying to pump over then there's no harm done.

Thanks for another suggestion, it took me awhile to figure out but i guess you mean tee the cold feed and vent together high in the airing cupboard for this "bypass circuit" but leave the tee from flow & return on cylinder pipes as they are.. Would this be prefferable to to a combined vent & cold feed as first suggested?

Have you done this in the past john? or anyone else tried it to success?

 

[John The Rad]

Yes, I've done this many times before combis came along.
It was a quick and easy way to sort when someone had fitted a system and left it pumping over with the obvious results, rusted radiators etc.
I always put a gate valve in the middle of the by-pass so I could control exactly how much by-pass to allow. I closed the valve then slowly opened it until the pump-over stopped.
Us oldies are "know it alls" you know.

 

[gassafe]

Thanks for another suggestion, I cant wait to try them out...

 

[John The Rad]

You're very welcome.

 

[John The Rad]

Let me know how you get on.