Trying to decipher a botched(?) c plan setup

[markptrueman]

Hi

This summer i'm looking to upgrade my archaic central heating to something like the Drayton Wiser system. The current system is as follows - seems to be C-plan with gravity hot water and pumped CH

Worcester Danesmoor 15/19 oil fired boiler
Grundfos CH pump
Potterton EP2002 timer
Frost stat.
Latchwell 2 port valve (really old)
Cylinder Stat
Single room stat in front room
No TRVs on any of the rads

I've been trying to decipher the wiring and it seems to be pretty messy, especially on the HW side of things

Boiler has only 2 wires connected (closest cable in the below image) - live to terminal 3 on the timer (HW on) and neutral to the neutral block. This implies that the boiler comes on whenever the HW is called from the timer and under no other circumstances (other than the frost stat calling for heat also, but that never happens).

Ive confirmed that the cylinder stat does nothing in terms of turning off the boiler when it isnt calling for heat, in fact, the cylinder stat does not seem to run anywhere. The two port valve also appears to do nothing. The wiring to those two is very strange.

The fixed live (twin and earth) that goes into the Ep2002 (the switched plug below), also goes off to the airing cupboard above, which contains the 2 port valve and the cylinder stat. The box on the left in this pic is a junction that runs off to the room stat for CH and seems to work fine(ish), it turns on the pump when calling for heat.

The live feed comes into the top of the junction box below. Out of the bottom right is the connection to the cylinder stat and out to the left is the connection to the 2 port valve.

This is the bit i really dont understand. This seems to be just a live feed and neither of the things connected to it does anything. Maybe the 2 port valve is broken and the idea is that the stat drives only the valve? Anyone got any insight into this and what it is attempting to do?

Once i can understand this, I would like to understand what i need to do to get the Drayton Wiser system in place by putting wifi TRVs on all new radiators throughout the property.

Thanks

Mark

 

[Exedon]

Just get the Wiser fear and rewire as needed.
If you really want a C plan diagram (or any other honeywell plan) Just download Honeywell home wiring guide to your phone.
Everything you need plus trouble shooting guide.

 

[ian1182]

I don't believe Drayton Wiser supports a gravity HW system. My understanding is that the HW and CH both need to be pumped on Wiser. Hive does have an option for gravity HW systems which basically means the HW comes on whenever CH is selected.

 

[markptrueman]

I don't believe Drayton Wiser supports a gravity HW system. My understanding is that the HW and CH both need to be pumped on Wiser. Hive does have an option for gravity HW systems which basically means the HW comes on whenever CH is selected.

Ok thanks for pointing that out. I'll take a look again although i thought as long as you had a cylinder stat and a 2 port on the HW feed into the cylinder you were ok. Would be interesting to understand why the wiser system treats the stat->valve calling for boiler and pump different to it just calling for boiler (as it would in my case), ie, why is pumping hot water to the cylinder different to the way it works now.

 

[ian1182]

Ok thanks for pointing that out. I'll take a look again although i thought as long as you had a cylinder stat and a 2 port on the HW feed into the cylinder you were ok. Would be interesting to understand why the wiser system treats the stat->valve calling for boiler and pump different to it just calling for boiler (as it would in my case), ie, why is pumping hot water to the cylinder different to the way it works now.

I believe the underlying issue is that Wiser does not have an option for the HW to come on whenever CH is selected. With a C-Plan system, the boiler is fired up when the HW comes on and the pump starts when CH comes on. The EP2002 requires HW to be on whenever CH is on. With Wiser the demand for HW and CH are independent, you can have HW only, both HW & CH or CH only. If only CH was on, then the pump would run but nothing would flag the boiler to start. It may be possible to adjust the wiring to accommodate but I'm not aware of how that is achieved.