advice on two HW cyclinder set-up.

[Norcon]

A little odd to say the least , where would you suggest hot supply to shower pump is connected?

Salamander S flange.

 

[commercialman]

A little odd to say the least , where would you suggest hot supply to shower pump is connected?

Salamander S flange.

Bearing in mind 'most' unvented cylinders use compression fittings for hot draw off it would be pretty much impossible for the dip tube on S flange to pass into cylinder.

 

[Norcon]

Good point.
But you just spec an appropiate connection to the manufacturer.

OSO have a dip tube and I removed one once which I think revealed a 1" bsp female if my memory serves me correctly.

What I do remember well was needing a 3 foot lever on a stilson to shift it.

 

[CharteredEngineer]

My suggestion would be to purchase an unvented steel cylinder in the capacity that you require (300L?) but run it with your current gravity fed tank.

A little odd to say the least , where would you suggest hot supply to shower pump is connected? , a little difficult trying to cut an essex/surrey flange into an unvented cylinder.

This might sound controversial but I would go direct off the 22mm feed on the side of the tank (NOT THE TOP). If you get something with multiple port tappings then the idea is to stop the air entrainment, with an unvented cylinder 66% of the way up should be sufficient, if you've got a dip tube then even better. They are pressure vessels so have dished heads, going off the top with only 2-3m of head will entrain the air. If you go off the side (like a Viessmann Cylinder - you can also get a dip tube for this, but may need to order from Germany), this will almost negate this problem.

I agree fitting flanges would not be possible with an unvented cylinder but in my opinion it is better to use a single unvented cylinder (with a dip tube) without a surrey/essex flange than a vented cylinder with a balancing valve.

The balancing valve will negate the effect of a surrey flange and you will lose NPSH and flow into the pump = recipe for cavitation.

 

[mellie_man]

To fit two motor valves only requires draining the heating circuit to the floor level on the floor with the tanks for a few minutes before refilling it.

Two hours for a DIYer and one hour for a pro.

The wiring and thermostat will take longer and will either need a control cable to the boiler or if thats difficult a wireless link can be used.

Tony

Hmm I see.
The tank stat is already linked to a valve down with the boiler (along with one valve for lower 2 floors, one for upper two floors and one for the kitchen UFH). the suggestion would be to leave existing value open and install the valves near the tanks (though there isn't much room at the moment, could be re-plumbed a bit).
wireless a no-go, c1900 house with proper walls and steels everywhere, plus 3 floors between.

 

[doitall]

Have you checked how hot the storage tank gets, as you have a perfect gravity circuit

The cylinders need a common cold feed.

A reverse return on a secondary circuit.

 

[mellie_man]

Have you checked how hot the storage tank gets, as you have a perfect gravity circuit

The cylinders need a common cold feed.

A reverse return on a secondary circuit.

One tank is foamed so can't check that cylinder , or did you mean the CW tank.
Cylinders CW feed comes from same CW tank connection but pipe is split about 1m after exit.
'A reverse return on a secondary circuit' not sure what you mean here, sorry.

AGILE 'fit two motor valves', found an alternative - a tapstat on the uncontrolled tank to prevent overheating. It won't prevent under heating (i.e. existing stat closing existing valve at boiler) but would protect the pump and possibly bring up to Regs.
http://www.discountedheating.co.uk/..._Drayton__Individual_28mm_2_Way_Tap_Stat.html

 

[commercialman]

No boiler interlock with tapstat , not a good idea with your set up , nasty things too , reverse return won't be much help here bearing in mind primary returns will have to be throttled down anyhow,

 

[doitall]

Assuming the OP has a secondary circuit, a reverse return will be very beneficial as it will equal the temperature of the two cylinders for a starters.

If you only have one storage tank connection that splits to both cylinders, it is fine and how it should be.

When you said two cold feeds I thought you meant from the storage tank, which is wrong and would have caused a circulation and a red hot storage tank.

 

[mellie_man]

I'm getting a pro in tomorrow, so it would help if I completely understood some of this terminology

commercialman 'No boiler interlock' means? - that it doesn't shut the boiler off?!

doitall ' reverse return on a secondary circuit', lost me on that one, please explain.

as I see it I have two options

1 cheaper/quicker - join tanks with an essex flange on each and tee off middle. Add a stat (tapstat or stat + valve) to stop overheating of non-controlled cyclinder.

2 better but more expensive - replace set-up with one 250L cyclinder and new surrey/essex flange, no worries.

CW tanks are only 50Gal, but spoke to a plumber today and he said he had never had a system that actually needed any more than that even with two pumped showers. Thoughts?

 

[commercialman]

replace set-up with one 250L cyclinder and new surrey/essex flange, no worries.

CW tanks are only 50Gal, but spoke to a plumber today and he said he had never had a system that actually needed any more than that even with two pumped showers. Thoughts?

Fill time of storage cisterns will be dependant on water main pressure/flow rate , can always fit an additional ballvalve to increase fill time.

250/300 litre open vented hot water cylinder would be the best way forward , not necessary to fit surrey/essex flange to these cylinders as they have provision for a 1" BSP secondary draw off.