How to test boiler with NEST

[Pste]

Hi,

Had Nest 3rd gen in for over a year now and my hot water function has stopped working (heating works fine). When I try to boost the hot water via the thermostat I can hear a click in the Nest heat link but the boiler doesn't actually fire up. Does this click mean it is doing everything required to request hot water or does it just confirm its received the incoming message from the thermostat?

Basically I want to know if the issue is with the boiler or Nest and I cant see anyway to just turn the hot water function on from the boiler directly (Logic Heat 12 Gas Boiler). Do i just need to move my wire that is currently in the Nest 6 port to the L port?

Thanks in advance

 

[stem]

Do i just need to move my wire that is currently in the Nest 6 port to the L port?

If your installation doesn't have a wire in Heat link (4) 'Hot Water Satisfied' then yes you could do that [Systems with 2-Port motorised valves]

If your installation does have a wire in Heat link (4) 'Hot Water Satisfied' then no you can't [Systems with a 3-Port motorised valve]

If you do have 3-Port motorised valve, it's actually the cylinder thermostat that is responsible for switching the boiler on / off when hot water only is operating. But it does get its live feed via the Heat link.

 

[Pste]

Thanks for the quick response, I do not have anything in 4 so I will try feeding the 6 direct to L and see how I get on.

 

[ianmcd]

Thanks for the quick response, I do not have anything in 4 so I will try feeding the 6 direct to L and see how I get on.

Doing that will bring the boiler on but probably wont heat the HW, sounds like the HW zone valve is faulty

 

[Pste]

After futher testing it appears its not NEST at least, I am able to heat my hot water now but only when the heating is on.

This never use to be the case, im guessing a switch/valve elsewhere has been changed by accident?

 

[ianmcd]

on the side of each zone valve is a manual lever, with a call for that valve the lever should be able to be moved across with no resistance, with no call the lever can still be moved but there should be a resistance is this the case ?

 

[stem]

Inside each valve is a small switch that operates the boiler. I would guess that the sequence of events could well be:

1) The HW valve opens, but is not operating the internal switch as it should, so therefore the boiler doesn't operate, and the water doesn't heat up.
2) When the heating comes on, the heating valve opens and its internal switch now triggers the boiler.
3) Because the HW valve is still open it now also gets water from the boiler, but only whilst the heating valve keeps the boiler running, as soon as the heating goes off, the boiler stops again.

 

[Pste]

on the side of each zone valve is a manual lever, with a call for that valve the lever should be able to be moved across with no resistance, with no call the lever can still be moved but there should be a resistance is this the case ?

This is correct:

Call for heating and hot water - both no resistance
No call for either - resistance on both
Call for heating only - resistance on hot water only
Call for hot water only - resistance on heating only

 

[stem]

Resistance means that the valve is closed, no resistance and it's open.

The tests show that the Nest is opening the valves correctly as it should, but it would appear that the HW valve is not starting the boiler when it's open. So my above theory of the faulty internal switch is looking likely.

 

[ianmcd]

This is correct:

Call for heating and hot water - both no resistance
No call for either - resistance on both
Call for heating only - resistance on hot water only
Call for hot water only - resistance on heating only

Then your nest is working correctly, sounds like a faulty micro switch in the HW zone valve, can also be a lazy motor that opens the valve but not far enough to make the end switch, some you can just swap the actuator head but not all, post a pic of your HW valve and I will tell you if you can just change the head without draining anything