3 port valve woes....again!

[rbrstr]

So. my sunvic SDM 1901 3 port failed and after seeking advice on here i have replaced it yesterday with a honeywell v4073.

unfortunately, the room stat does not fire up the boiler at all,ever, and the boiler seems controlled entirely by the tank stat, which leaves the boiler nearly constantly on. leading to tropical climates and scolding HW

i have triple checked all the wiring,( i took a photo before i touched the old wiring) and the a,b,ab orientation is correct

any help? before i thow in the towel and call a plumber, cant really afford it but there you go

 

[matt1e]

So. my sunvic SDM 1901 3 port failed and after seeking advice on here i have replaced it yesterday with a honeywell v4073.

unfortunately, the room stat does not fire up the boiler at all,ever, and the boiler seems controlled entirely by the tank stat, which leaves the boiler nearly constantly on. leading to tropical climates and scolding HW

then it isn't being controlled by the cylinder stat then, at least not correctly

i have triple checked all the wiring,( i took a photo before i touched the old wiring) and the a,b,ab orientation is correct

I would quadruple check the wiring, what are you using to test with
some pics of your connections may help

Matt

 

[Ihavenojob]

The sunvic SDM is a MOMO valve & is not compatible with a V4073 as it is a spring return valve.

 

[matt1e]

The sunvic SDM is a MOMO valve & is not compatible with a V4073 as it is a spring return valve.

momo.... yes
incompatible.... NO

The honeywell valve will be fine