Flow- Vent- Feed -Pump

[Madrab]

Open Vent (OV) is intrinsically safe as it runs @ atmospheric pressure and properly set up and looked after then it is perfectly fine, less stress oon components/fittings. Sealed allows the open vent, feed, cistern etc to be removed and can be a little more straightforward to install though safety devices are required - Expansion Vessel (EV) & Pressure Release Valve (PRV) plus a means to fill.

Sealed, I would suggest is easier to DIY than OV is as there is a bit of theory and technical specific setup needed to setup an OV system properly but as long as you follow the rules then it's either or.

 

[desktop987456]

Thanks, Is there a specific reason for fitting a non return valve in Feed Tank?
Existing pipework doesn't have a separate vent pipe going over the Feed cistern/tank. My open flue boiler was setup this way and has worked fine for years.
Do I need to install a 22mm vent pipe separately?
My understanding is that feed pipe from tank serves as a vent pipe as well but with non return valve in tank how would it vent?
I am just clarifying a few things for understanding and trying to make things right in case they have setup incorrectly.

 

[fixitflav]

Thanks, Is there a specific reason for fitting a non return valve in Feed Tank?

I'm not aware of any reason for a NRV in a feed tank.

Do I need to install a 22mm vent pipe separately?
My understanding is that feed pipe from tank serves as a vent pipe as well

I'm not keen on it, but combined feed and vent is possible. But that would be going away from the system in the photo in your original post.

 

[Madrab]

Thanks, Is there a specific reason for fitting a non return valve in Feed Tank

If you didn't have an up and over vent pipe into the feed cistern (F&E) and only the one feed pipe then it sounds like it was set up, as suggested, as a combined feed and vent, if that was the case then it shouldn't have had a NRV installed, as that basically removes the safety vent and stops the system from 'breathing' - as the system heats up it expands into the cistern, cools down then that expansion returns to the system, so not sure what your system was doin if it was open vent but had an NRV in the feed. Combined feed and vent is usually introduced due to system limitations or bad design and removes a pumping over issue. There is a risk though that the feed could stop the system venting if a problem occurs.

An up and over 22mm expansion vent is the standard safety feature of an open vent system, if it ever enters a runaway overheat condition, it's a basic design principle of an OV system.

 

[desktop987456]

but combined feed and vent is possible

Which is I beleive what I have from F&E tank through a small dia copper pipe which looks 15mm to me.

An up and over 22mm expansion vent is the standard safety feature

Yes, I have seen it in all reading material that I have gone through and wondered why I haven't got one. I looked at the old boiler and it has a PRV installed on flow pipe, I think I found the answer on NRV and combined vent & Feed in my pipework?

 

[desktop987456]

The pump needs to be placed after the feed and vent with the flow away from them to keep the system under positive pressure. The boiler can really be fitted anywhere in the chain, if it's a HO but there are more favourable positions for it, depending on the system layout

Its a heat only boiler and as you say pump needs to be placed after f&V pipe with flow away which means into rads. My system layout is such that 9 rads are where the system is going to have positive pressure (in theory) but a couple of rads are on opposite side of f&v pipe as well, does this mean that there could be less flow or no flow situation to those two rads in case of inadequate pumping power in proposed setup at first floor?

Secondly, the return line to boiler will also be teed after the same positive pressure system point but on return line or it doesn't matter?

There is nothing mentioned in Viessmann manual in installing a PRV but if I remove the non return valve from tank which will serve as f&v (no separate vent pipe), would it be safe to install a PRV on flow on boiler? I have attached old setup drawing (1st photo at Ground Floor) and new boiler to be setup at first floor (2nd photo). In the new boiler setup there has to be no direct feed from head tank to flow inlet of boiler? The boiler HEX takes it water from flow pipes.

Please have a look and let me know if this is correct. Thanks

 

[Madrab]

If you have a PRV then that would point towards it being sealed rather than an open vent but if it's gravity fed by a cistern that's open to the atmosphere then that would be more like an open vent system, all a bit confusing. Not sure it that's a US quirk. I think you may want to take it back to a standard to ensure everything works as it should, sealed or OV. You don't want any valves incorporated into the feed or vent or combined, as suggested though a combined isn't a standard, it's really implemented to fix issues/badly design systems that are drawing in air or pumping over.

but a couple of rads are on opposite side of f&v pipe as well,

you want to avoid having any rads in between the feed and vent and the pump, they will work but the system will need to be finely balanced.

Secondly, the return line to boiler will also be teed at the same positive pressure system point but on return line or it doesn't matter?

Not quite sure what you mean? anything prior to the feed and vent will be under positive pressure, it's only at the feed that it changes to negative. On a 2 pipe system then one pipe is the flow and the other the return so the return shouldn't have to 'tee' into anything, if you see what I mean. The only tee that would be incorporated would be the return from the cylinder, if and when it's added (apart from the feed and vent of crse)

 

[desktop987456]

Not quite sure what you mean? anything prior to the feed and vent will be under positive pressure, it's only at the feed that it changes to negative. On a 2 pipe system then one pipe is the flow and the other the return so the return shouldn't have to 'tee' into anything, if you see what I mean. The only tee that would be incorporated would be the return from the cylinder, if and when it's added (apart from the feed and vent of crse)

Thanks, extremely helpful comments. Sorry if this confuses you but I wanted to confirm the return piping connection to boiler (see blob in pic dotted path to return inlet of the boiler)

 

[Madrab]

That's a very convolute design setup, I would recommend you look at it again and try and 'flow' the 2 pipe system a little more direct than that to make it as easy as possible to setup and maintain the system properly. In that pic it seems you are pumping towards the feed rather than the feed entering the flow prior to the pump, so not the best. That will take a very precise balancing exercise to ensure it all heats up properly.

As a starting point you would look at something like this for the feed (and vent), that way the only part of the system that's under neg pressure is between the feed and the pump.

 

[desktop987456]

I am with you, not the best job with the drawing, sorry if it confuses you. To simplify it further:
- vent pipe added, Teed from feed tank
- feed point is Neutral point of the system.
- As you say the section between feed and pump inlet is under negative pressure
- pump location showing inlet to the pump; and is pumping away now (downward from feed)
- where do I add return line to boiler's inlet port?

Really appreciate your inputs.

 

[fixitflav]

Its a heat only boiler and as you say pump needs to be placed after f&V pipe with flow away which means into rads. My system layout is such that 9 rads are where the system is going to have positive pressure (in theory) but a couple of rads are on opposite side of f&v pipe as well, does this mean that there could be less flow or no flow situation to those two rads in case of inadequate pumping power in proposed setup at first floor?

Secondly, the return line to boiler will also be teed after the same positive pressure system point but on return line or it doesn't matter?

There is nothing mentioned in Viessmann manual in installing a PRV but if I remove the non return valve from tank which will serve as f&v (no separate vent pipe), would it be safe to install a PRV on flow on boiler? I have attached old setup drawing (1st photo at Ground Floor) and new boiler to be setup at first floor (2nd photo). In the new boiler setup there has to be no direct feed from head tank to flow inlet of boiler? The boiler HEX takes it water from flow pipes.

Please have a look and let me know if this is correct. Thanks

In your Pic1, boiler with integral pump is a system boiler, and AFAIK always has an integral expansion vessel, so F/E tank not needed. But it's possible to use a F/E tank, in which case I believe the connection should be to the boiler return, which is as close as you can get to the pump suction.

In Pic2 the vent is not shown and the feed is in the wrong place. It should be as Madrab shows in #24

 

[Madrab]

Always valve your pump inlet and outlet in case it ever needs replaced, also easier to connect to the system due to the pumps flange sizes.

Looking at the previous pics too, if you had a boiler with an integrated pump, as @fixitflav mentions, the newer ones like that tend to be system boilers, but you mentioned yours was an open flue'd appliance, given it's the US though it may have been different. System boilers though typically would have the pump and an expansion vessel in the case. Adding to that the pressure relief valve (PRV) that's been found and the NRV, then that would point towards a sealed system. Just because the system was fed from a cistern doesn't mean it wasn't sealed, though usually the filling loop would be from the mains but again not sure how it may all differ in the US.

What was the previous boiler? Your current boiler is a UK/EU version? So it's the WB1A (13Kw)? Can I suggest you go and download the installation manual for the boiler - it shows a great picture of an open vent Y Plan system which you are proposing.

 

[desktop987456]

In your Pic1, boiler with integral pump is a system boiler, and AFAIK always has an integral expansion vessel, so F/E tank not needed.

- Pic 1 is currently what I have in terms of boiler and pipework. The boiler didn't have an expansion tank inside it; F&E was placed over on 1st floo

In Pic2 the vent is not shown and the feed is in the wrong place. It should be as Madrab shows in #24

Roger.
What about the return line to the boiler?

 

[desktop987456]

but again not sure how it may all differ in the

I inherited the heating system and boiler and can confirm that what you have summarized is the case.
I bought the UK version of the boiler, its a 13kw heat only boiler WB1B 2018 model. I have the manual.
The part I wasn't clear about was do I need to change the existing feed to the boiler and other connections to existing pipework. see 2nd photo of the feed from tank to the existing pipework and how to make other connections to the boiler.
I will be removing the existing feed and will modify the pipework as per manual.

 

[fixitflav]

- Pic 1 is currently what I have in terms of boiler and pipework. The boiler didn't have an expansion tank inside it; F&E was placed over on 1st floo

Boiler with pump but no exp vessel is a new one on me, but we live and learn! I don't know whether system boilers have the pump on the flow or the return, or some of each, but in any case I would put the cold feed on the return pipe, preferably close to the boiler. If you use a separate vent, put it 150mm or less before the feed (flow-wise). Where it's shown there is a chance of getting negative pressure at some point.

What about the return line to the boiler?

It's shown on Madrab's #24. I agree with that.

BTW if you're thinking of installing a HW cylinder in future, don't forget all the rad returns must be commoned before the cylinder return connection. Might affect how you plan the rad piping.