suitable new programmer?

[suzieb]

Our CH is a fully pumped system with 2 pumps , not the usual 1 pump plus motorised valves.

The programmer we have allows us to set HW and CH times totally separately. The programmer is old and now seems to have gone haywire, so we need a new one.

Plenty to choose from, but although they all say suitable for fully pumped systems, they only seem suitable where there is one pump plus motorised valves.

Is there a programmer that can do what we want?

 

[D_Hailsham]

Are there two separate pumps or are they combined in a single body (Grundfos PumpPlan)?

 

[suzieb]

2 totally separate pumps, both Grundfoss.

 

[D_Hailsham]

2 totally separate pumps, both Grundfoss.

OK

Which make/model programmer do you have now?

 

[suzieb]

It is a 23 year old Maplin Universal Timer with 4 output channels so you can time HW and CH either on a weekly or 5/2 day basis by switching between channels 1 + 2 and 3 + 4, or each day can set individually. Multiple on/offs can be set for each day. So it is not a programmer specifically designed for controlling heating systems.

The output from the timer goes to the boiler and pumps via 3 x 12v relays. There is also a frost stat connected.

 

[D_Hailsham]

The output from the timer goes to the boiler and pumps via 3 x 12v relays. There is also a frost stat connected.

I thought there would have to be relays, to prevent back-feed from one pump to the other.

So the output of the timer is 12v?

If so, is that AC or DC?

What supplies the 12v is it the Maplin Timer?

Presumably everything is connected into a junction box.

 

[suzieb]

Yes, the output from the timer is 12v, 12v DC.

OH is the one who understands the details, but there are 2 boxes set in the wall, one where wires come in, marked 240v, and one where wires go out again . The components in this area are marked 12v DC.

Inbetween and fitted over these is a backplate holding a board with various components and the 3 relays , and loads of connections between various wires. There is also a plug that the timer itself connects to . The timer sits on the front cover part that slides over the backplate and is screwed in place.

I hope this is making sense!

 

[DP]

Any programmer will work (my choice would be FP715) and one relay will be needed (not three) and the relay will need to have 240 volt coil.

You existing setup can be modified for use with 12 volt relay (as already mentioned only one relay needed) and an opto coupler.

 

[suzieb]

Could you givev a bit more detail on that?

As it happens, we purchased an FP715, but we obviously need to alter the relays too.

 

[DP]

Ch ON programmer contact goes to roomstat, switched live of roomstat goes to NC contact of a relay as well as CH pump.

HW ON programmer contact goes to HW stat. Switched live from this goes to HW pump and NO of said relay. Relay coil (240 volt) is connected to this point as well. Alternative if using 12 volt relay is to use opto isolator for mains isolation with LED side having suitable dropper resistor and diode. Again, details available

C of relay contact goes to boiler.

OR, use satchwell relay box.

If none of abovea good for you, use FP975 for voltage free switching, or one TS715 and one programmable room stat again these will give you voltage free contacts as will Honeywell ST699 programmer.

I trust you are handy with a multimeter and circuit wiring as what you have (is already evident) needs tweaking and simplified.

 

[suzieb]

We do not have a roomstat. The system (it's old) works only on thermostatic valves and boiler stat. We do have a HW stat, and a frost stat.

I presume that will alter things?

Will pass your comments to OH, who is very handy with the multimeter!

 

[JohnD]

are the motorised valves 22mm or 28mm?

I only did this once, but the 28mm has an extra wire in the head

the stat opens the motorised valve, and the valve, when open, turns on its pump with this extra wire, so no relay required.

 

[suzieb]

No, we do not have any motorised valves.

We have a boiler, 2 pumps, thermostat on HW cylinder, frost stat, timer/programmer, thermostatic valves on all but one radiator (this to act as bypass, it is a small rad in a big hallway).

At present we can set times on HW and CH totally different if we wish.

 

[JohnD]

no room stat?

 

[suzieb]

No, all done with thermostatic valves and boiler stat. Not today's best practise, but it works well with the house layout, so we don't really want to change that right now.