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Great to find a forum like this, hope I can get some help. Just moved house and find this place has a decent Valliant boiler controlled by a Sunvic Programmable Thermostat

Have spent the last couple of days figuring the thing out and have got my schedule and desired temperatures all sussed. However, the thing doesn't seem too responsive e.g. it won't turn the boiler on when the room gets too cold at the designated times, and vice versa. Seems to need a kick up the backside to get it going i.e. manual override temperature right up.

I think it could be this optimum start feature, so I'd like to know how to disable it. The literature on the Sunvic webby isn't any help. There is no 'link 1' or any jumper nodes. The only thing that seems changeable on the inside is a small box of 3 switches on sw10 that can be on or off. I can give you a picture if you like.

Anyway, any help greatly appreciated as the mother is getting irritated by the fact the house is still freezing at 6am despite the fact it's all set to bring it up to 20oC!




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  • #2
wired to normally closed N/C instead of normally open N/O?? would mean that when the temp is too low and the stat is trying to call for heat it'd make it open circuit, therefore boiler wouldn't come on. only time it'd close the circuit and switch the boiler on is if the desired temp was reached; which won't happen unless you override the boiler somehow.

wild stab in the dark. pics are always good :)


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  • #3
Thanks for the effort Grae79, much appreciated. I think it's all wired ok though. Basically it won't call for heat unless the temperature is substantially below the desired temperature, and won't turn the boiler off until the room is substantially over the desired temperature - about 2 degrees C.

In the morning when the house is at 16oC and comfort mode kicks in, asking for a temperature of 19oC, it comes on but won't switch off until the house is at 21oC.

In the afternoon when the house is at about 18oC and comfort mode comes on, it won't switch the boiler on unless you override it and push the temperature up to 20oC or so.

Very annoying. I think it's this Optimum Start nonsense, but I can't figure out how to turn it off.

I'll try to get some pics later today when I get home.

Thanks again though :)


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  • #4
here's what sw10 does: (default is all on)
switch 3 is heater/cooler (on for heater)
switch 1/2 set the temperature differential (how much the temperature has to change to kick the heating in,

both on = 1 Deg C diff(0.5 below = on, 0.5 above = off)
sw1 off and sw2 on = 2 Deg C diff
sw1 on and sw2 off = 3 Deg C diff
both off = 4 Deg C diff

There is apparently no Optimum Start on this model - I got the instructions by e-mailing them, you can get them here

So it looks like you might have 1/2 off rather than on (you have to reset the thermostat for changes to these switches to take effect)
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