Ufh Controller And 3 Port Valve Conundrum

I've been asked to rewire a heating system.

It's under floor heating downstairs and radiators upstairs.  conventional indirect hot water tank.

It's plumbed with a 3 port mid position valve to select HW, heating or both.

Now the tricky bit.

The UFH controller has it's own built in programmer.  It also has the facility to control the hot water times.

But at the moment, none of that is used and there's a conventional boiler programmer as well.

the customer wants the extra programmer removed and everything controlled from the UFH controller.

The available connections on the UFH controller are:

"HW thermostat" (two terminals for the tank stat)

"HW valve or pump" (N and switched L out)

"Boiler enable" (a volt free contact)

So the way it's supposed to work, is whenever hot water or heating is called, the volt free "boiler enable" contacts will turn on and fire the boiler. (not used at the moment, the boiler firing is controlled from the 3 port valve and tank thermostat, but it's not working properly)

Whenever the UFH programmer calls for hot water AND the HW cylinder stat is closed, the "HW valve or pump" output will be energised.

So here's the tricky bit.  How to make that work with a 3 port mid position valve.

I can't see any way, as the conventional circuits require a "Heating OFF" signal which we don't have.

And I don't think suggesting he re plumbs it to use two 2 port valves instead is an option.

All I can think is a relay or two.

I throw it open to the forum to suggest something better.

Pinched this of another forum, has the word "relay" in it:

Install enclosure and SPDT relay :- 

Connect boiler feed to common terminal.
Connect central heating switchwire ( orange ) to N/C terminal.
Connect underfloor heating switchwire ( orange ) to N/O terminal.
Use underfloor heating switchwire ( orange ) to power relay coil.

Will admit not having thought about it. I have a traditional system with one 3-port and two 2-ports (up and down heat zones) and will shortly doing some ufh, All the fun to come!

Thanks.  I'll draw it out and see if that makes sense.

That`s no use - its more of an override to operate the boiler. . . . . . . 

Hang on.............

The ORANGE wires, unless i`m going stupid, come from the microswitch in the valve (along with the grey)

So simply joining the two orange wires together as the boiler feed would do the same thing!!!!! There`s no feedback to consider.

Right - so back to the problem.

Dave - have I missed summat? Where will the upstairs CH be controlled from? I`m reading that they want to control everything from the UFH controller, which has DHW inputs.

3 port valve......AS2..............

Right.

Its not a "heating off" you`ll be wanting - its a DHW off I think (unless they`ve set the 3 port up wrong!)

In which case - using a tank stat with a "satisfied" output should give you the "water off" signal you need.......no it won`t; unless you have a relay, with coil fed from the "HW on" - you could get your "HW off" from the n/c contact............

But I still come back to - where are you controlling the 1st floor CH from??

Upstairs heating will come on whenever any downstairs heating is on.  It's simply teed off the flow / return to the UFH manifold.

So there's no controls to the upstairs rads. but they do all have TRV's.

If that proves unsatisfactory, then I could wire one of the spare "UFH zones" (there are two spares) to an upstairs room stat. That would ensure the UFH controller keeps the boiler calling for heat, even if all the downstairs UFH zones were satisfied.  But anyway, that's a seperate issue.

Anyway, attached is my first attempt at a scheme.

I've used a relay to turn the "hot water demand" into the required "no hot water demand"

I've used the presently unused UFH zone 7 with it's thermostat linked out, to give me a "heating on" output from the UFH controller.

There's one more thing shown that I forgot to mention.  for some reason that escapes me, the plumber has also fitted a "energise to close" 2 port valve in series with the hot water flow.  that seems completely pointless to me as I can't see what it does that the 3 port valve does not. but anyway I've aranged for that to be energised as well whenever there is no hot water demand.

EDIT:

I can't do anything "clever" with the normally open contact of the cylinder stat, because if I'm reading the manual correctly, the UFH controller sends 12V DC to the cylinder stat, and switches a relay on it's board to generate the "hot water valve or pump" signal.

Note also, in my scheme, I don't need to use any of the feedback contacts from the motorised valves. that's because the UFH controller has relay logic built in to call for heat from the boiler whenever heating or hot water is demanded.

John_1.pdf

kme said:

Its not a "heating off" you`ll be wanting - its a DHW off I think (unless they`ve set the 3 port up wrong!)

Click to expand...

As KME said..

Y-plan has Heating ON  Water ON and water OFF signals..

Hot water ON via tank stat is a direct signal to boiler by-passing the valve as the valve will be sitting in the home/return position..

The Water OFF signal helps drive the valve fully to the heating only position when both white & Grey are live ..

it is only when Both water & heating need to be on that the valve is stalled mid position with the Heating On signal up the white wire.

You won`t get "water only" from that, will you? As the water on supply is from zone 7..................

Besides - 12V to the tank stat is ok - you can use a relay with 12V coil..........

The zone valve in the water is probably to prevent heat bleeding to the cylinder under gravity, when heating is on; though its normally on the heating upstairs, to inhibit the upstairs rads heating through gravity when DHW is on.

If its definitely in the water line, I`d be tempted to manually lock it open; and / or utilise the "open" microswitch into the DHW boiler firing cct - save pumping into nothing as & when the valve fails!

kme said:

You won`t get "water only" from that, will you? As the water on supply is from zone 7..................

Besides - 12V to the tank stat is ok - you can use a relay with 12V coil..........

Click to expand...

That;'s the sort of comments I'm looking for.

BUT when a 3 port valve is de energised, it relaxes (by spring) to the "Hot water" position doesn't it?

So the UFH controller calling for "hot water" will create a boiler (and pump) demand, and that will flow through the relaxed 3 port valve to the tank.

When the tank stat opens, the UFH controller will stop sending the boiler demand and it will turn off.

The Zone 7 output is to tell the "system" when heating is demanded as well, to move the 3 port valve to it's mid, or heating position.

Or have I completely miss understood how 3 port valves work?

I am generating the "water OFF" signal sourced from Zone 7 (it could in fact be any L supply) but that is only relevant when heating is on as well as hot water anyway, so that seemed a logical place to source it.

I've updated the circuit. In my haste, I had got the relay connection a bit wrong.

I've also added some more labels to make the function of wires more obvious.

Do you think this will work?

John_1.pdf

Do I understand you got no separate thermostat for the Upstairs rads..?

just the downstairs UFH???

Surely you would need the UFH to come on well before any upstairs rads due to the time taken to bring the floor up to temp....

{its a cooler temp running UFH that the water in the upstairs rads..}

Also I would have thought you would probably need separate time zones for them to be coming on?

also isn't there another circulation pump just for the UFH..?

Cant see off your drwg if or where this is??

Maybe you should convince the customer that what they want to do, and what should be done are slightly different.

3 Channel Programmer, 3 Zone Valves, Stat for Rads, Cyl Stat for Water and UFH Controller and relevant stats triggered by programmer.

This system really should be an S plan plus (three zones each with a self closing 2 port valve)

Anytyhing else is a bodge really. The ufh really needs to be on much longer than trad rads.

Plumbers just seem to think they have to fit 3pv's to everythng!

Just thinking around this again...

There may be a simple solution, assuming Cylinder and 3-port valve are close together....

But need to recap some facts..

1/ The hot water can be all worked OK from a signal from your UFH controls Yes?

& as the 3-port only needs to be in home position for this the water on signal by-passes the valve anyway.

2/ You can get a Heating signal from your UHF controls to drive the 3-port to the midway stall position, by the heat only with the white wire. Yes?

3/ All you need to do is provide a means to fully drive the 3-port valve by sticking 230v on the Grey wire,  if the water is already hot and the heating needs to be on as well?

By adding an extra tank thermostat..  (which includes a nice SP change-over switch)

You could bridge white and Grey wires across this extra tank stat so whenever the tank is hot and the heating is on the 230v you are putting to the white is also going to the Grey to drive the valve fully.

If the tank is to cold the valve will sit in the midway posn by the signal on the white.

BUT..

this is making a basic assumption that the customer would never want the heating on

whilst having no hot water sitting in the tank! 

and

The position and heat setting of this second tank stat could give a bit of flexibility.

It could save time messing with 12v & relays...

:C

Thanks for the above.

the crucual thing is the normal 3 port valve circuit needs a "hot water off" signal but the UFH vontroller only gives a "hot water on" hence the need for the relay.

Yes the UFH controller has a specific timer function for controling the hot water, but it's outputs are limited (no hot water off signal)

It would all work easilly by converting to 3 2 port valves, but customer has specifically stated no plumbing alterations, he just want the wiring "sorted out"

I can't easilly fit an extra cylinder stat.  It's a megaflow indirect tank, so it's not just a case of scrape off some of the lagging and strap a stat on. It would need to be a capillary stat in a pocket, and I don't even know if there is a spare pocket to add a second stat.

Now can I throw in the "final" part of the "problem"

Water is ALSO heated by an aga, and a wood burning stove.  These, along with the boiler feed into a neutraliser, and the output from the neutraliser feeds the the tank and the heating.

There's a thermostat strapped to the neutraliser. The idea being nothing starts flowing until the neutraliser gets hot, so this currently turns the circulating pump on and off.

And one more thing. He wants to use the aga and wood burner as much as possible, with the oil boiler only as a backup.

That throws two extra problems into the equation:

Firstly I  can only think of a manual switch to enable or disable the boiler.

Secondly, when using a wood burner to heat a tank, there MUST be somewhere to dump heat of it gets too hot. So that's really looking like I MUST find a place for a tank overheat stat to dump heat to the radiators if it's getting too hot.

Agree.

The solid fuel units would be best served with pipe stats, to inhibit the oil boiler when flow pipes from aga or wood burner are hot - that`s not a big problem.

The neutraliser is already thermostat`d, to inhibit pump flow until neutraliser reaches operating temp.

I like SL`s idea for the tank (I`m assuming this is a vented cylinder? If its unvented, you need to be really careful - dunno about Scotland, but we`re supposed to have an unvented qualification before worlking on `em!)

If you`ve only one stat pocket - this will become a really convolved control system. I`d envisage either relay banks, or a PLU to handle the various states of inputs a,b,c, etc - to control the outputs as ordered by the logic.

Cylinder heat dump: You / customer might want to consider a dedicated heat dump radiator - rather than heating the whole system up. We did that on one job - the customer complained that 30 mins after lighting the wood burner, the upstairs was reaching silly temperatures, and they couldn`t turn it off!!!!!

Im getting lost here, but are you allowed a solid fuel appliance heating a unvented tank? 

wozz said:

Im getting lost here, but are you allowed a solid fuel appliance heating a unvented tank? 

Click to expand...

That's actually a very good question.

The best way to organise multi source heating systems is with a heat store tank, but crucially those are fed from a header tank so no unvented tank issues.

But you might well be right. Feeding a wood burning stove into an unvented tank would rely on a thermostat and a pump to dump heat. If there's a power cut (which is just the time you would be using the woodburner on full tilt) then there's nothing, apart from the over pressure and over temperature vent, to stop the tank becoming a bomb.

This is beginning to look like a can of worms I might not want to open.  although I didn't plumb the system (and would never do it that way if I did) is it a case of the last person to work on the system becomes responsible for it's safety?  If so I may walk from this one.

Im sure a heating engineer mate said a solid fuel appliance couldnt be used with unvented due to G3.

On the other hand fitted one of these the other day you might be interested.

http://www.h2panel.co.uk/

I would say that you CAN, because of the neutraliser, acting as a "low loss header" ( I believe is the correct phrase)

HOWEVER. You MUST fit the heat dumps to the primary of the solid fuel units, and fit 2 port valves to the coil(s) of the cylinder.

It used to be the case that solid fuel was a definite no-no, but not any more - though I would clarify this.

As long as the source of heat can be separated from the cylinder - you don`t have a problem in that respect.

But I`m thinking that a thermal store might be the way forwards..............................