Vaillant combi, danfoss thermo. Sometimes heating does not come on.

[baggister]

I have a Vaillant combi (kitchen) and a danfoss thermo (not n wall, I leave it lying around). Sometimes the boiler does not come on for the heating for a long time (hot water fine).

Eg now it's pretty chilly this morning, the heating is not on. I press up on the Danfoss until it shows 20.5 , and nothing happens. 10 minutes later, still nothing. The Danfoss display still shows 20.5 and has a little flame icon. Pressed up again until it shows 22.5. Nothing happens for about 2 minutes, then it comes on.

It's more noticeable when I come back from a week away on holiday: I can push it to 22.5 and nothing whatsoever happens for at least 24 hours.

Sometimes it's perfectly fine.

Any ideas please?

 

[cross thread]

replace the batteries and check if the receiver by the boiler is responding to the signal

 

[baggister]

replace the batteries and check if the receiver by the boiler is responding to the signal

Just tested the two duracell AAs on a voltmeter, dishing out 1.5v each. (Brand new ones I have tested at 1.6 each) , so I dont think there's anything wrong with the AAs.

How to tell if the receiver is responding? Isn't it inside the boiler itself?

 

[ianmcd]

How to tell if the receiver is responding? Isn't it inside the boiler itself?

might be on the boiler facia might not post some pics of the boiler facia and anything attached to the boiler

 

[baggister]

Took these, let me know if you need more. Thanks for your help btw.

 

[terryplumb]

More pics of below the boiler,follow any wires from it.

 

[baggister]

I can see two wires but not sure I can get to where they go.

 

[terryplumb]

Why ,what's below the boiler ?

 

[Harry Bloomfield]

Just tested the two duracell AAs on a voltmeter, dishing out 1.5v each. (Brand new ones I have tested at 1.6 each) , so I dont think there's anything wrong with the AAs.

Near dead AA's can test at 1.5v on a high impedance meter. For a reliable indication, they need to be measured with some load across.

 

[CBW]

Cables look buried in the wall, so post a photo of the receiver. Also when it next fails, try pressing any rectangle button to wake the screen up, then press the top 2 rectangular buttons together, and report back what the s code is please. Also is the heating temperature up high enough on the boiler display?

 

[baggister]

Near dead AA's can test at 1.5v on a high impedance meter. For a reliable indication, they need to be measured with some load across.

Thanks - just followed your advice 2 minutes ago: I used the probes across one AA while both AAs were in the thermo and clicked up to get it transmitting, meter displayed 1.52v. Oddly enough , sometimes went to 1.53v. Tried across both batteries, got 3.07v. Interestingly enough, hard to get the needle probes to touch one of the contacts, and occasionally the screen went blank when forcing the probe, so one of the batteries does feel a tad loose. I could put a bit of aluminium foil in there to "snug" things up. having said that, when I press up during the time when nothing happens, the display is never blank. Pretty sure there's nothing wrong with these duracell AAs.

 

[baggister]

Why ,what's below the boiler ?

 

[baggister]

Cables look buried in the wall, so post a photo of the receiver. Also when it next fails, try pressing any rectangle button to wake the screen up, then press the top 2 rectangular buttons together, and report back what the s code is please. Also is the heating temperature up high enough on the boiler display?

Sorry dude, don't know where the receiver is.

When you say "pressing any rectangle button to wake screen up", do you mean the buttons and screen on the boiler itself?

As for heating temperature up high enough on boiler display, I don't know. What should it be?

 

[baggister]

Thermo just crashed, the buttons not responding at all, and it seems to display numbers even without batteries (internal battery keeps it going for a bit I'm guessing. Crash must have happened while probing around. Anyway, hard reset done, back to normal.

 

[baggister]

Cables look buried in the wall, so post a photo of the receiver. Also when it next fails, try pressing any rectangle button to wake the screen up, then press the top 2 rectangular buttons together, and report back what the s code is please. Also is the heating temperature up high enough on the boiler display?

I wil try to get the S code next time as it happens rarely, except for when returning after a week away on holiday when the heating does not come on for at least 24 hours when manually pressing up or down. (I don't think there are any timer events)