Nest Gen 3 Hot water does not work

[Mal-110]

Hi,

Just had nest fitted by qualified electrician. We have a Viessmann 100w boiler on an open vented Y plan system. Heating working fine. The domestic hot water claims it is working but does not heat up the cylinder. I have switched off the heating and tried just the water, although the circulating pump works there is notstart up from the Viessman The radiator symbol is visible on the boiler screen but not the tap (indicating hot water) The nest schedule is set and does indicate bright orange as if the boiler is heating domestic hot water. I checked on the app and saw that hot water off/on was greyed out so I slid the button over to highlighted blue. Thought this would do it but no. Checked boiler no tap symbol, pump on but no hot water.  On the thermostat itself schedule is in place and its enabled. Any ideas what might be wrong?  Electrician claims all wiring is correct and has been tested!

[Frustratedddd]

Just to get my head round this, you are trying to get hot water only, without the rads getting warm?

You call for hot water only, you hear the pump, but the boiler does not come on?

[Mal-110]

Not necessarily hot water only, but I would like the gas boiler to heat the water cylinder at some point. Heating is working as per schedule. The thermostat and app both show hot water is on, the pump is on but the boiler won't fire up. The heatsink clicks and the pup starts. The thermostat on the cylinder is set to temperature but the water remains cold.

[Frustratedddd]

Your heating is working, got that.

Are you saying the hot water tank is not getting warm at all?

[Mal-110]

Yes, The boiler won't fire up when the thermostat and heatlink call for heat.

[Frustratedddd]

Sounds like a wiring issue to me.

The heat link has 2 contacts, one for heating, the other for hot water. You may find the water connection in the heat link is wired wrong. The contacts are normally open or normally closed. Depending on the way the heat links been wired could well be the problem.

You should be able to call for hot water and the boiler will come on, but NOT the pump.

Does that make sense?

[Mal-110]

It does make sense. Electrician coming back on Tuesday. The pump should come on to circulate the water in the cylinder coil.

[Frustratedddd]

Ah yes you have a combi, sorry, I was thinking the heating pump for rads.

I think you will find the contacts are staying open or the wiring is round the wrong way for the valve to open on call.

[philipo54]

have the same issue but it has suddenly stopped working, been ok for 5months so i don't think its wiring issue

[Mal-110]

Electrician came back and rewired the connection to the hot water cylinder thermostat and we now have hot water. The initial wiring worked for the previous controller but not for the nest. 

[Jwal24]

I  just getting this exact same problem now. This is a year after having nest installed. So surely can’t be wiring. I am currently in Scotland on holiday and it’s my elderly mother who’s stuck with no hot water. Radiators are hearing fine….