Top-up bottle

[Mark K]

So that's fine I would install a nrv on the feed and then just install all you safety things minus the filling loop

Thank you, great to have it confirmed. I add the filling loop later if I want to, or decide to do away with the header tanks to free up loft space. For now the ball valve on the vessel manifold is a nice comvenient drain point .

 

[Mark K]

I have read your plans very carefully, I would make an initial,observation that 65% of all sealed unvented systems leak and lose pressure so an unconnected Top up bottle could be a pain, and mains water at pressure is very cheap.
Unless you are worried about wras regulation regarding seperation of drinking water etc. I can quote you chapter and verse if you need to know
I am a heating designer so can see where you are coming from.
But why design problems in ?
I also fail to understand the motivation behind your project
So,perhaps you might elabourate (they can’t touch you for elaborating I do it )
Rob Foster

Thanks Rob,

The house I bought in 1994 was a small cottage, with no heating or hot water. I installed a boiler in the cornerof the 8' x 8' kirchen and, because there was no space I put the cold water tank, f and e tank, hot water cylinder, pump and S plan valves in the loft.
Primary flow went from the boiler, past tje vent pipe, past the fande through the pump and into the S plan valves.
The house is 2.5 times the size now and what was the cornerof the kitchen is the middle of the lounge and the boiler is in the garage, which didn't exist back then.
I have added two radiators in the, now, kitchen, (to replace electric underfloor heating) and connected into the f and r primarys for 2 reasons. First, it saves ripping the house apart and second, so I can have it as a seperate zone. With the pump in the loft, A, the heating or hw would need to be on to get circulation so it could only be a zone that could be off, not on by itself. B, the circulation could/would bypass the boiler. So I moved the pump to the flow directly above the boiler. But that puts the pump before the vent and f and e connections.
Again, moving those involves pipe runs in the decorated part of the house, so I decided to make it a sealed system.

It's almost just an acedemic interest thing for me to know if I can use the f and e tank as a top up bottle, permanemtly connected via a nrv.

I have oversized the expansion vessel slightly to reduce the pressure rise and only filling to atmospheric pressure via the top-up bittle seems a good move too.

 

[Mark K]

Ok Mark, point made now stop poking the bear eh?
(pun intended lol)

Yes, agreed, I was quite upset. Calmed down now.

 

[Mark K]

Using the existing F & E tank how would you achieve the initital system pressure?
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Edited
Scrap that question , it was open vented so won't have a minimum requirement.

That is my understanding, also, as the boiler has top outlets, the chance of damaging it, or causing a danger, from running dry is minimal, unless the boiler itself fails, then it's damaged anyway, and that's no different to a vented system.

 

[Mark K]

Lever valve rather than gate valve? More reliable.

Indeed, but there is already a gate valve on the outlet from the F and E tank.

I know, I know, there shouldn't be.

 

[Rob Foster]

Yes, agreed, I was quite upset. Calmed down now.

Ok so we are all back on track
Now, Imwill,look at this again when I get gnome
Rob Foster aka centralheatking

 

[Mark K]

Ok so we are all back on track
Now, Imwill,look at this again when I get gnome
Rob Foster aka centralheatking

Hi Rob,

This explains a little better. Excuse my technical drawing, a bit rusty these days.

Cheers,

Mark

 

[Gasmk1]

why not fit one of these in plave of the tank and set at 1/2 bar you can get them with a guage easy to do

Emmeti UK - 00200514 - 1/2" MBSP x FBSP - Automatic Filling Valve - 00200514

 

[SimonG]

Personally I would go filling loop and do away with tank and just pressurise to half a bar.

 

[Mark K]

why not fit one of these in plave of the tank and set at 1/2 bar you can get them with a guage easy to do

Emmeti UK - 00200514 - 1/2" MBSP x FBSP - Automatic Filling Valve - 00200514

Never seen one of those, every day is a school day. Thank you.

 

[Mark K]

Personally I would go filling loop and do away with tank and just pressurise to half a bar.

I may well do exactly that, and in the fullness of time will change the HW cylinder as we are in a hard water area and that would be an ideal time to do away with both header tanks and go mains pressure HW too.

Initially I want to see what the standing pressure is at the vessel when filled as a vented system and note that as a benchmark. I suspect it may be about 0.6 bar because of the height of the tank.

Then I will know what pressure at low level would definitely fill the system.

Am I thinking correctly there? As you fill an empty system the pressure increases first with the water column and then once full against the expansion vessel and interior of the system, until it reaches mains pressure assuming it doesn't burst?

Or did you mean put the filling loop in the loft and pressurise there to half a bar?

 

[SimonG]

Filling loop somewhere easy accessible. If I fit an external boiler I will fit a gauge and a filling loop inside.

 

[chris watkins]

Perfectly sensible idea to use an existing Feed cistern to continue to automatically top up a now sealed system with the same low pressure it always had on it.
It is often shown in MI's as an option, you will note a check valve is required on the cold feed to create the seal (as you stated you have capped the old vent pipe). It is surprising that some engineers have never seen the diagrams in the boiler instructions!!
Where is the expansion vessel located ? Its gas charge will need to be adjusted to equal the static water head above it, as 1M = 0.1bar you can work it out before you refill the system with water.
One thing to remember is that the point of connection of the vessel will now be the neutral point of the system so ideally it should be located on the suction side of the pump so that as much of the system is under positive pressure as possible.
Just for your info the 418 is a regular or heat only not a system boiler that would be a 618.

 

[chris watkins]

Only other problem you are going to have is rads getting hot in the summer as you have broken the last tee rule ie. return from cylinder must be the last connection before it goes back to the boiler.

 

[Mark K]

Perfectly sensible idea to use an existing Feed cistern to continue to automatically top up a now sealed system with the same low pressure it always had on it.
It is often shown in MI's as an option, you will note a check valve is required on the cold feed to create the seal (as you stated you have capped the old vent pipe). It is surprising that some engineers have never seen the diagrams in the boiler instructions!!
Where is the expansion vessel located ? Its gas charge will need to be adjusted to equal the static water head above it, as 1M = 0.1bar you can work it out before you refill the system with water.
One thing to remember is that the point of connection of the vessel will now be the neutral point of the system so ideally it should be located on the suction side of the pump so that as much of the system is under positive pressure as possible.
Just for your info the 418 is a regular or heat only not a system boiler that would be a 618.

It's a heat only boiler, you are quite right. The expansion vessel is on the boiler return about 400mm before, the pump is directly on the flow, to keep it as far from the first bend as possible, so only 400mm of pipe and the boiler are between the suction side of the pump and the vessel.

The MI for that boiler actually lists the mains filling loop as an option to the top up bottle.

I reckon the header tank is 6m above the boiler, hence my estimate of 0.6bar at the gauge on the expansion vessel.

I had picked up on the need for a check valve.

It is still running as a vented system right now, I will connect in the vessel, blow off valve, cap the vent and install the nrv on the feed all at the same time. Until I was certain I understood what and why I was doing, I put up with a bit of pump over.

Thank you for your advice.

 

[Mark K]

Only other problem you are going to have is rads getting hot in the summer as you have broken the last tee rule ie. return from cylinder must be the last connection before it goes back to the boiler.

Agreed, I will have to live with that, or turn individual rads off.

Do you think that will be different with the new pump location, as it hasn't been up to now?

 

[chris watkins]

If Rads are fitted with TRV's they might be stopping it.
It is not an exact science anyway.

 

[Mark K]

If Rads are fitted with TRV's they might be stopping it.
It is not an exact science anyway.

Thanks,

To be honest, it was installed in 1994 and the HW was put in first, so it may well not be exactly as I have shown.

TRYs are fitted too.