Does anyone have a diagram of how a system with 2 pumps and no valves is
wired together to give interlock? Secondly how does pump overrun work if 2
pumps are used (i assume you have to dump into the CH cylinder)

Does anyone have a diagram of how a system with 2 pumps and no valves is
wired together to give interlock?

Very simple. Wire the programmer output through the appropriate room or
cylinder thermostat to the pump. The same connections should also be made to
a relay. The Normally Open outputs of the relay should be connected together
in parallel and be used to run the boiler interlock.

Secondly how does pump overrun work if 2 pumps are used (i assume you
have to dump into the CH cylinder)

This gets a little more complicated. You basically need the pump overrun
output of the boiler to run the hot water pump. However, it is essential
that this doesn't end up as a call for heat back at the interlock, or it
will never switch off. You also don't want the HWC pump to run when the CH
pump is running, or the HWC will overheat.

Let's draw a logic diagram:

Inputs:
HWC = hot water call for heat (from thermostat/programmer)
CHC = central heating call for heat (from thermostat/programmer)
POR = pump overrun from boiler

Output:
HWP = Hot water pump
CHP = CH pump
BIL = boiler interlock
(T) = should be impossible or transient condition only


HWC CHC POR | HWP CHP BIL
0 0 0 | 0 0 0
0 0 1 | 1 0 0
0 1 0 | 0 1 1 (T)
0 1 1 | 0 1 1
1 0 0 | 1 0 1 (T)
1 0 1 | 1 0 1
1 1 0 | 1 1 1 (T)
1 1 1 | 1 1 1

(Alternative for DHW priority)
1 1 0 | 1 0 1 (T)
1 1 1 | 1 0 1

This gives

HWP = HWC OR ( POR AND NOT CHC)
CHP = CHC
BIL = HWC OR CHC

So, connect CHC directly to the CHP pump.
BIL is run by paralleled relays from HWC and CHC.
HWP is harder, but can be done with a few relays.

To be honest, I'd be inclined the run the whole control system in low
voltage logic (i.e. 5V 74LS/74HC) and end up in a nice relay for the boiler.
But then, it would be simple for someone like me to throw together something
on a bit of stripboard with a 7805, a wallwart and a handful of SSI logic
chips.

Christian.

In message , Christian
McArdle writes
Does anyone have a diagram of how a system with 2 pumps and no valves is
wired together to give interlock?

Very simple. Wire the programmer output through the appropriate room or
cylinder thermostat to the pump. The same connections should also be made to
a relay. The Normally Open outputs of the relay should be connected together
in parallel and be used to run the boiler interlock.

Secondly how does pump overrun work if 2 pumps are used (i assume you
have to dump into the CH cylinder)

This gets a little more complicated. You basically need the pump overrun
output of the boiler to run the hot water pump.

So where does the heat go if the taps are turned off?

Didn't you mean the central heating pump ?

--
geoff

This gets a little more complicated. You basically need the pump overrun
output of the boiler to run the hot water pump.

So where does the heat go if the taps are turned off?

Didn't you mean the central heating pump ?

No, the pump for the hot water primary circuit is more suitable for pump
overrun than the central heating circuit. Don't get confused with the DHW
secondary, which is isolated from the primary system.

Christian.

In message , Christian McArdle
writes
This gets a little more complicated. You basically need the pump overrun
output of the boiler to run the hot water pump.

So where does the heat go if the taps are turned off?

Didn't you mean the central heating pump ?

No, the pump for the hot water primary circuit is more suitable for pump
overrun than the central heating circuit. Don't get confused with the DHW
secondary, which is isolated from the primary system.

So where are you dumping the heat to if there is no DHW flow ?

--
geoff

So where are you dumping the heat to if there is no DHW flow ?

The cylinder itself. Although already at a high temperature (i.e. 60C), it
still acts as a nice energy dump, especially as the flow temperature rises.
Even if the flow temperature rises to 90C (unlikely), thats a nice 30C
difference across the heat exchanger and the cylinder won't get appreciably
hotter because of 30 seconds of overrun with the burners turned off.

Christian.

It can actually all be done with a single relay (with Double pole change
over contacts). I have been working this out over the past few days.

Relay coil goes across the CH Pump.


Boiler overrun contacts.
Boiler overrun live goes to NC contact.
Heating Demand Live geos to NO contact.
HW Pump Live goes to Common.

Boiler control Contacts.
Heating Demand Live geos to NC contact.
Unswitched Live goes to the NO Contact.
Boiler switched Live goes to common.

Someone may be able to do an ASCII art version of this, It's beyond me.

Christian McArdle wrote:
Secondly how does pump overrun work if 2 pumps are used (i assume you
have to dump into the CH cylinder)


This gets a little more complicated. You basically need the pump overrun
output of the boiler to run the hot water pump. However, it is essential
that this doesn't end up as a call for heat back at the interlock, or it
will never switch off. You also don't want the HWC pump to run when the CH
pump is running, or the HWC will overheat.

Boiler overrun contacts.
Boiler overrun live goes to NC contact.
Heating Demand Live geos to NO contact.
HW Pump Live goes to Common.

Boiler control Contacts.
Heating Demand Live geos to NC contact.
Unswitched Live goes to the NO Contact.
Boiler switched Live goes to common.

Someone may be able to do an ASCII art version of this, It's beyond me.

Yes, I think that works!

Inputs to system:
CH On = Central heating on (at programmer)
HW On = Hot water on (at programmer)
POR = Pump output (from boiler)
N = Neutral
L = Permanent Live

Output from system:
BCFH = boiler call for heat

Pumps:
CHP = central heating pump
HWP = hot water pump

Switchgear:
rts = room thermostat
cts = cylinder thermostat
NO = normally open terminal
NC = normally closed terminal
C = common terminal
/\/\ = relay coil

/
CH On O---o o-------+--CHP---+---O N
rts | |
+--/\/\--+

Thanks Christian

I realised after I'd posted that I left out some detail but you have
added it.


This is slightly different from my previous "ideal" (number in bracket is
the difference), but should still work perfectly. The effect is not to start
the hot water pump directly in response to a hot water heating demand.
Instead, the system waits until the boiler's pump output is activated, which
should happen as the BIL input to the boiler has activated.

However the conventional single pump system does that anyway!

I bet someone comes up with a system that doesn't use a relay at all, but
just changeover thermostat terminals...

I think you need a doupble pole switch somewhere to make it work. Can
be either thermostat though.

In an earlier contribution to this discussion,
Clive M wrote:

Does anyone have a diagram of how a system with 2 pumps and no valves
is wired together to give interlock? Secondly how does pump overrun
work if 2 pumps are used (i assume you have to dump into the CH
cylinder)

I don't have an official diagram, but I've just drawn one on the back of an
envelope which I think will work. If I describe it, you should be able to
replicate it. I will deal with only the live connections, leaving you to put
in all the neutrals and earths.

On the left is the programmer, with feeds for HW and CH
To the right, one above the other, are the cylinder stat and room stat. Both
are normally closed switches, opening when the set temperature is reached
To the right of these is a mains changeover relay
To the far right is the boiler

Take a wire from the programmer's HW feed to one side of the cyl stat
Connect the other side of the cyl stat to the HW pump and to the NC contact
of the relay
Take a wire from the programmer's CH feed to one side of the room stat
Connect the other side of the room stat to the CH pump, the relay coil, and
the NO contact of the relay
Connect the relay's Common terminal to the Boiler switched live
Connect a permanently live feed to the Boiler permanent live
Connect the Boiler Pump terminal to the NC relay contact (and hence to the
HW pump)

If I am right, this will fire the boiler - plus the appropriate pump
whenever either the CH or HW or both are demanding heat, and will shut down
when neither is.
If the boiler's pump over-run stat operates, the HW pump will run until
things cool down.

I can see one potential problem with this, which may require a mod to the
boiler's internal wiring. On my boiler, the pump outlet is connected to
switched live below the boiler stat temp, and to permanent live above the
stat temp. My diagram, as it stands, would result in the HW pump running
whenever the boiler was on - even if the HW demand was satisfied. Severing t
he internal link between switched live and pump would do the trick - only
allowing the *boiler* to switch the pump on *above* the stat temp.

HTH.

--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"Clive M" wrote in
:

Does anyone have a diagram of how a system with 2 pumps and no valves
is wired together to give interlock? Secondly how does pump overrun
work if 2 pumps are used (i assume you have to dump into the CH
cylinder)

I've considered the Grundfos Pump Plan - seems very advantageously priced
at plumbworld ATM, and came up with this doc

UPP_Pump_Plan_05_03.pdf

but I don't know where from.

It contains a wiring diagram.

I think they also sell a complete control pack, which I would be tempted to
use if I were installing it.

I really like the idea, but it's a bit bleeding edge for me...., what
happens if one pump fails in a cold snap?

mike

"mike ring" wrote in message
52.50...
"Clive M" wrote in
:

Does anyone have a diagram of how a system with 2 pumps and no valves
is wired together to give interlock? Secondly how does pump overrun
work if 2 pumps are used (i assume you have to dump into the CH
cylinder)

I've considered the Grundfos Pump Plan - seems very advantageously priced
at plumbworld ATM, and came up with this doc

UPP_Pump_Plan_05_03.pdf

but I don't know where from.

It contains a wiring diagram.

I think they also sell a complete control pack, which I would be tempted
to
use if I were installing it.

I really like the idea, but it's a bit bleeding edge for me...., what
happens if one pump fails in a cold snap?

What happens if a zone valve packs up?

In an earlier contribution to this discussion, mike ring
wrote:

I've considered the Grundfos Pump Plan - seems very advantageously
priced at plumbworld ATM, and came up with this doc

UPP_Pump_Plan_05_03.pdf

but I don't know where from.

It contains a wiring diagram.

A URL would be *awfully* useful!



I really like the idea, but it's a bit bleeding edge for me...., what
happens if one pump fails in a cold snap?

You lose *either* the HW *or* the CH - as opposed to losing *both* with a
conventional one-pump setup!
--
Cheers,
Set Square

"Set Square" wrote in :


I've considered the Grundfos Pump Plan - seems very advantageously
priced at plumbworld ATM, and came up with this doc

UPP_Pump_Plan_05_03.pdf

but I don't know where from.

It contains a wiring diagram.

A URL would be *awfully* useful!

http://www.centralheating.co.uk/inde...ewFile&id=6551

I hope it works, took ages to find again,


I can't find any reference to prevention of flow if only one service is
required - if the CH is on ISTM that the pump will pull water through the
boiler, but also tend to pull it back through the HW circuit.

Otherwise I'm very rempted, the price isn't too outrageous against one pump
and a 3port or two two port valves, and it seems more direct.

I realise 2 pumps in one casing means quite a lot of replacement for one
failure, but I haven't found grundfos pumps bad

mike

In an earlier contribution to this discussion,
mike ring wrote:

"Set Square" wrote in
:


I've considered the Grundfos Pump Plan - seems very advantageously
priced at plumbworld ATM, and came up with this doc

UPP_Pump_Plan_05_03.pdf

but I don't know where from.

It contains a wiring diagram.

A URL would be *awfully* useful!

http://www.centralheating.co.uk/inde...ewFile&id=6551

I hope it works, took ages to find again,


I can't find any reference to prevention of flow if only one service
is required - if the CH is on ISTM that the pump will pull water
through the boiler, but also tend to pull it back through the HW
circuit.

Otherwise I'm very rempted, the price isn't too outrageous against
one pump and a 3port or two two port valves, and it seems more direct.

I realise 2 pumps in one casing means quite a lot of replacement for
one failure, but I haven't found grundfos pumps bad

mike

Thanks for the link. Looks interesting! May not be too easy for diy-ers to
diagnose if the integrated logic goes wrong.

As far as I can see, you still have two water circuits with a common feed
from the boiler. I can't see any reason why either pump should induce any
flow in the other circuit. However, there is nothing to stop gravity
circulation if either circuit decides to do its own thing.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"Set Square" wrote in
:


Thanks for the link. Looks interesting! May not be too easy for
diy-ers to diagnose if the integrated logic goes wrong.

As far as I can see, you still have two water circuits with a common
feed from the boiler. I can't see any reason why either pump should
induce any flow in the other circuit. However, there is nothing to
stop gravity circulation if either circuit decides to do its own
thing.

But one pump is fed not only from the boiler but from the other circuit,
unless there's something to prevent backward flow, as the are common at the
input of both pumps, and at the boiler return which would be at a higher
pressure.

I admit I don't know for sure, but having sketched it out, I'm more
convinced;

The gravity bit is the other thing; in the absence of any forced flow,
would the hot water cylinder cause a flow through the rads and cool itself
down?

Of course the maker prolly knows what he's up to - I just wish I knew more
before taking the plunge

mike

mike ring wrote:


I can't find any reference to prevention of flow if only one service is
required - if the CH is on ISTM that the pump will pull water through the
boiler, but also tend to pull it back through the HW circuit.

The pump plan pump has the anti backflow valves built into it.