thermal store

[hosegood]

I have a woodburner connected to a gledhill thermal store. I have copied an exsiting system as close as poss.
I have two radiators connected, one 3meters long and the other 2.5 meters long. When the pump switches on it sucks a liitle water from the header tank and when the pump turns off the water is replaced via the vent pipes. This in itself is OK but over a period of time the water in the tank gets quite hot and can overflow. The problem will also happen when the system is cold.
One rad has 22mm pipe right upto the last few feet, the other one has 22mm then 15mm to the last 4 feet
any ideas? Please
Laurel

 

[hosegood]

It has been sugested that air in th system is compressing when the pump goes on which pushes back the water when the pump goes off. Does this make sense?

 

[Biggles..]

You posted the exact same question the other day under a different user name,why not use those answers.

 

[hosegood]

Did you read those answers?
They were from a couple of guys who were mucking about
This is a serious problem I have
The name was a typo its Laurie

 

[Norcon]

A line drawing of the layout would be handy.

 

[hosegood]

Thanks
I will do a drawing but I can not until tomorrow
Laurie

 

[Biggles..]

If your post is genuine I hope you get an answer,my doubts
Over how genuine these posts are, are simple, normally we see probably 1 post a fortnight about thermal stores, with the recent trolls and thermal store salesmen joining the forum we're seeing 2/3 posts a day.

 

[Agile]

Laurel, surely you must realise that your system is not operating correctly?

Furthermore, sucking water will also suck oxygen which will corrode the innside of the rads, cause corrosion and result in sludge! See FAQ on sludge!

Tony

 

[hosegood]

This is a genuine problem. The system is brand new and not being used full time yet (because of this problem) also 2 more rads are to be added.
As I said I copied another system which works OK, although the other thermal store is not quite the same spec, but almost.
If I am sucking water down the feed pipe is oxygen getting into the system?
I have done more tests by closing each rad and I get more water back into the header tank from the smaller rad than the bigger one.Very strange.
Thanks for your replies
Laurie

 

[hosegood]

Attached is a crude diagram of my system View media item 39177

 

[Norcon]

Back to the drawing board. No cold feed!
Which gledhill store do you have?

 

[SimonH2]

At the risk of asking the obvious ...

you have used the right ports for the CH loop haven't you ?

Other than that, I can't really see how it's possible to pump over with that setup. You are right to be worried though, pumping over will keep oxygenating the system and accelerate corrosion.

 

[hosegood]

Thanks for comming back
The cold feed is 22mm from the F&E tank to the bottom of the Thermal Store. The tank is a Gledhill Torrent indirect OV.
The ports are all labelled by Gledhill and the pump is connected to the flow (top port)
When the pump goes on the level in the F&E tank drop very slightly and when the pump goes off the water is replaced via the vent pipes, both the tank and woodburner vents. I left the pump on for a while today (cold) thinking that the levels would stabilize but it didn't and the same thing happened.
It is worse with the rad on the 1st floor same level as the TS, the rad on the top floor does not have this problem.
I have jacked up the rad slightly to see if there is air trapped, as they are very long, but nothing there.
The only difference in the plumbing of the two rad is that the smaller one has 15mm pipes at the last 1.5 meters
thanks

Untitled

• hosegood
• 1 Nov 2011
• 1

 

[Norcon]

Try lowering the pump speed down.
Also looking at the diagram you seem to have an "open pipe" by pass back to the store so maybe the pump is creating negative pressure at the top of the store.

 

[SimonH2]

Try lowering the pump speed down.
Also looking at the diagram you seem to have an "open pipe" by pass back to the store so maybe the pump is creating negative pressure at the top of the store.

Yes, the bypass is an issue - but not for this problem. I'd suggest getting rid of the bypass, fitting a modulating pump (eg Grundfoss Alpha II), and fitting TRVs on all rads - and dispensing with the room stat if there is one. That way, each room is individually controlled by it's TRV and the system is virtually silent.

The pump cannot create negative pressure in the store. Depending on the arrangement of the ports, I guess it's possible it's creating some dynamic pressure imbalances, but given the size of these things I find that a bit hard to believe.

Have the rads been bled ? If there were a lot of air in them, and the lockshields weren't fully open, and the pump is on high, then I could see the pump pressuring the air and thus needing some water from the F&E tank to maintain system volume. When the pump shuts off, the air will expand back to it's normal volume, and this needs to get back to the F&E tank via the feed line. I guess inertia means some goes that way, some goes up the vent pipe.
Another question, how high above the water level do the vent pipes go, and is there space to extend them ?