Wiring a flow switch for CH

[Peter B]

Afternoon folks,

Using the S-Pan Plus wiring diagrams from the Wiki as a basis

how would I wire a Gentech FS-05 flow switch into the setup so that when flow is detected the boiler fires?

I have a UFH manifold that operates as a closed circuit when a call for heat is received from its programmer/stat, running the pump that circulates water through the manifold. When the temperature on the return manifold drops, a thermostatic valve opens up the injector valve on the flow side to bring in new hot water and it's this flow that I want to sense to fire the boiler, if you follow.

The user guide for the manifold suggests that _ordinarily_ the prog/stat would connect back to the main wiring centre itself and fire the boiler when there's a call for heat, but it struck me that if there's sufficient heat still in the manifold loop, the injector valve will still be closed and the heat from the boiler will have nowhere to go .. correct?

[Toby]

If the boiler was called by the thermostatic valve that opens up the injector valve when the UFH is on, and is up to temperature, surely that would be OK wouldn't it?

Toby...

[Michael Chare]

If you put the flow switch between terminal 10 and the L on the boiler then the boiler would only run if there was flow.

The flow switch may have NO and NC contacts in which case use the NO contact pair.

This would stop the boiler in the event that the room is not up to temperature but the water in the manifold has reached its maximum. However that situation may not last for very long as if the UFL pump is running I would expect there to be a requirement for some heat input as the UFL pipes will be loosing heat.

You might want to discuss your proposal with a UFL equipment supplier.

[Peter B]

Unfortunately it's a purely mechanical thing; thermostatic head on a valve with a remote sensor on the end of a wire.

's no electrical connections to it, thus my idea to use the flow switch to detect the flow when the valve has opened and the manifold pump is pulling water through.

[Peter B]

Ah, no - that'd be no good as it would stop the other zones from working.

The equipment supplier in this case is whomever I buy the relevant bits from and I'm the installer. I'm trying to make the best out of the botch job that the "heating engineer" who previously owned the house cobbled together using (seemingly) whatever was left in the back of the van.

If you're really, really nice, I'll find you a picture so you can marvel at the "installation".

[Dave Osborne]

I have read all the other replies and I hafta say I can't comment on whether the flow switch is a good idea or not and where in the circuit you would want to put it, but I would offer this: -

The diagrams for flow switches in the Sundial PDF were drawn because in cheapie Farnell-supplied plastic flow switches (e.g.

), the switch element is a reed relay, which has a maximum switching current of 1A. Therefore, you need an intermediate relay to boost the switching capacity to a minimum of 3A to run the pump (or whatever).

The flow switch you have chosen already has a switching current of 3A because it has a triac built in, so you don't need an intermediate relay.

The connections to this unit (according to the data sheet) are "Form A triac", which basically means that the flow switch is like a domestic dimmer switch in that it only has two terminals, viz "live in" and "live out".

So, you connect the "live in" to permanent live and "live out" becomes live for the duration flow is detected.

HTH.

[Michael Chare]

Clearly you don't just have S-Plan then. Maybe in that case you also need to use a relay.

Equipment manufacturer then. I would have thought that your problem is common to any situation where there is UFL and other central heating.

[dennis]

> There's no electrical connections to it, thus my idea to use the flow

I would imagine it would be easier to find the plunger that moves to open and close the valve and fit a microswitch that operates when it moves. If you do do so use LV as it would be difficult to insulate it well enough for mains.

You could fit one of these but again I would use LV.

[Peter B]

A nice clear answer Dave, thanks.

So, with due apologies for bastardising your original diagram, would the following be a correct circuit?

interpretation/intention is that a call for heat at the stat would send live to both the manifold pump and the "live in" of the flow switch. The manifold pump should always run and when incoming flow is detected, the flow switch should send live to connector 10 on the wiring centre, which in turn fires up the boiler and its pump.

Job jobbed?

[ARWadsworth]

What manifold do you have? Usually there is another stat wired into the manifold to control the pump in the underfloor heating part. It looks to me like Mr Bodgit missed that out, but you should still be able to buy one.

Most manifolds for UFH (well the ones I have worked on) act as a bypass when the injector valve is closed.

[Michael Chare]

Which pump generates the 'incoming flow'?

[Peter B]

The UFH pump triggers the incoming flow when the thermostatic valve on the flow side of the manifold opens up. Until that valve opens, the water in the manifold loop just circulates round and round.

It all makes sense in my head, but that's not to say my head is screwed on proper :/

[Peter B]

The new manifold is a Hepworth, made by Giacomini - like this one;

Stat -> Manifold Pump

Hmm, you've got me wondering if I've mis-read the whole damn manual now and I'm coming at this completely arse about tit :) I'll have to take another look at it when I get in tonight. If anyone's got five minutes to spare, a second opinion would be welcome ...

[Dave Osborne]

Well, as I say, I'm no expert at UFH, and I don't fundamentally see why you have omitted a zone valve, unless the injector in the manifold does the job of a zone valve, in which case, the flow switch you are proposing does the job of the aux contacts on the zone valve.

So, as long as you can guarantee that the flow switch contacts being closed means it's OK to run the boiler (especially when *only* the UFH is calling for heat) then you're good to go, I would have thought.

Having said that, the above advice is worth every penny you paid for it!

HTH DaveyOz.

[ARWadsworth]

> Room Stat -> Manifold Pump

Down on page 40etc it shows how they have wired the UFH up to a zone valve.

So it looks like the boiler runs until it reaches it's internal stat temperature (that stat shown on the diagram if a safety cut). In that case you will be relying on the system bypass that a S Plan usually has when the injector valve is closed. That sounds like the setup you already have.

I wonder if you could use a pipe stat on the return pipe to turn the boiler off in a more efficient manner than your currrent set up. The pipe stat would need to be set just higher than the maximum temperature of the UFH.

[Peter B]

Their option E on page 42 is essentially the same setup as the manifold I've bought. The only difference is the safety thermostat, which is an option with mine, that I've not bought (yet) but can be added any time.

Its function appears to be to sit between the room stat and the manifold pump, and if the mechanical thermostatic valve fails and doesn't blend the flow temperature down, it cuts the manifold pump causing the incoming hot flow to just go straight out the on the return.

I'm still trying to weigh up the extra 85 quid on that one.

In all honesty I don't really have a setup of any kind at the moment - a blessing and a curse I guess. At the minute, there's the combi boiler, a timeswitch and one CH flow/return circuit.

The current UFH "manifold" hangs off that one circuit too, so to have the UFH running you're also feeding the radiators, whether you want to or not. Add to that there's no thermostat telling the boiler to switch off if the house ever gets to temperature. It's probably about as bad as you could get...

To give you a flavour, this is what lives under the landing floor;

orderly queues for laughter on the left and sympathy on the right %-)

Having read through a load of UFH suppliers documentation now, it would appear that this is pretty much the standard way that they mostly operate - call for heat from the boiler, but don't tell it if we don't need it anymore, well not until we shut down anyways. Seemed rather inefficient to me at the outset, which was why I was trying to come up with a means to only call the boiler when it was actually needed.

[ARWadsworth]

> Form orderly queues for laughter on the left and sympathy on the > right %-)

Obviously without any zone valves it is very inefficient. Especially as the UFH needs to be turned on many hours before the normal rads.

There also seems to be no way to balance the UFH loops.

[Peter B]

>>> Form orderly queues for laughter on the left and sympathy on the >> right %-)

Thanks. I've still got no idea what the trombone-style arrangement of pipes on the left-hand side is supposed to achieve...

.. or bleed air from it, or tell what temperatures it's operating at, or drain it and so on.

The whole system is being reconfigured as four zones, which might seem alot, but the UFH cuts the house in half and the areas either side have completely different heating profiles;

- one zone for the upstairs, controlled by a wireless prog/stat - one zone for the UFH, again under control of a prog/stat - one zone for the kitchen/scullery with another prog/stat - one zone for the bathroom, always open

The bathroom will get flow whenever any of the other zones are open, so should keep it nice throughout the entire day, given the differing times the other zones will be firing. Plus, it acts as the bypass when all zones are shut but the boiler's pump is still running, which I understand is both a modern requirement and common sense.

I *think* I've got it all straight in my head now, just got to turn it into reality. Apologies in advance for any dumb questions as I go ;)