Vaillant EcoTec 630 plus boiler turns on for central heating but not providing domestic hot water

[Neil10]

After the last few days of warm weather, the CH thermostat never triggered the boiler to turn on, and now the DHW temperature has dropped. I can't seem to get the boiler to turn on for DHW.

The boiler only shows the CH radiator symbol on the right, and no DHW tap symbol on the left. From reading the forums it seems that some of these boilers in fact do not have separate CH or DHW controls, but just provide heat, so maybe that is not a problem.

I can get the boiler flame to turn on by turning up the CH thermostat so the boiler seems to be working fine.

We have a controller for the DHW / CH which we have just always had on the 24 hour setting and have made no changes to. There also seems to be a DHW circulation pump with an attached physical timer with pegs set to 6 am and 11 pm.

Questions ...

1. Is it correct that these Vaillant boilers do not display the DHW tap symbol?
2. What mechanism is used to get the boiler to turn on for DHW? Is there some sort of easy fix to common problems with getting the bioler to turn on for DHW?
3. Lastly, what should the temperature be set at if the boiler is just providing heat for both CH and DHW? It is currently set at 75 degrees C.

Clearly something is broken because DHW used to work fine even when CH was not needed.

Thanks for any pointers. Total novice here.

 

[picasso]

The hot water One of these is probably faulty...

 

[Deleted member 267285]

Yep, agree with @picasso, and if you have a hot water cylinder, there will probably be a cylinder thermostat on this which is usually what controls your hot water temperature, but it's usually the motorised valve (pictured on Picasso's reply).

 

[Neil10]

Thanks @The Novice and @picasso . Much appreciated.

Continuing to poke around and reading up on internet while we try and find a plumber during the corona lockdown. Have looked at the pipework around the boiler and can see that from where the hot water comes out of boiler, via the pump, and then there is a Honeywell valve for the DHW and one for the CH for the radiators. I can trigger the CH valve to turn off by either turning the CH off (on our Centaurplus thingamagic with the CH and DHW controls - see picture), or by turning the thermostat inside the house down. I can't get the DHW valve to turn off if I turn the DHW off. I can feel the hot water flowing past the DHW valve to the hot water cylinder. So it is clear that that valve is not doing anything - but the important thing is that it is not closed. When the CH is on, the boiler is firing, and the hot water is flowing from the boiler past BOTH these valves.

The problem seems to be that when the CH turns off, the boiler also turns off, and the temperature of the water in the boiler drops, and even though water is still flowing past the DHW valve, it is not hot water going to the cylinder.

So the problem seems to be whatever mechanism is used to turn the boiler on when the water in the DHW cylinder drops in temperature. Whereas I can see the feedback loop for the CH (the thermostat inside the house sends a signal to the Drayton box on the wall (uploaded picture) which triggers the CH valve to open and ALSO fires up the boiler), I don't see what the corresponding mechanism is for DHW. What causes the boiler to turn on and off based on DHW temperature? There seems to be no feedback loop from the thermostat on the DHW cylinder to the boiler to turn it on.

So my novice view is that whatever problem happened was not noticed for a while since the CH has been on frequently enough to keep the DHW heated. And now that CH is no longer coming on, the boiler is staying off for days, and the DHW is also cold.

Anyways, for now we've turned the thermostat inside the house to 26 degrees, which has kicked the boiler on, causing the hot water to also flow past the DHW valve. Hopefully that will heat up the DHW cylinder while we look for a plumber to come by.

If there are any pointers on how we can get the DHW to heat up by getting the boiler to fire (the DHW valve being open as I said always, so it is getting the boiler to fire that seems to be the problem), please let me know.

Cheers.

 

[picasso]

The hot water valve has jammed in the open position but hasn't closed the microswitch inside it, the valve has a removable head so is an easy job to replace, don't over think the problem .

If you want hot water switch on the immersion heater or leave the heating on for an hour or so.

 

[Deleted member 267285]

The mechanism for controlling the dhw cylinder is a cylinder thermostat (strapped to the side of the cylinder), if the Honeywell valve isn’t doing anything at all, then it’s likely to have failed. If this is the case then the cylinder thermostat will have no effect, because the heating one is by-passing the valve anyway. You could try and turn off the main isolation switch (in your picture), however this may then cause the valve not to re-open, thus no hot water.