Vaillant 828/2 E NTC Fault?

[Richard2009]

Help - getting chilly!

Boiler:
Vaillant 828/2 E E Wall Hung Room Sealed Fan Assisted Combination Boiler

Set to timed operation to come on 05:30 am 'till 9am, then 4pm until 11pm

Symptoms:
Seems to come on in the morning ok. However doesn't come on in the evening, without some persuasion.

I thought it was a dicky timer, but I'm not so sure now.

Came home tonight to find it making the right pumping noises, but the radiator outflow was cold, but felt like it was flowing water ok. The boiler just hadn't lit up.

Switched it off at the main "On / Off" switch on the facia, and then back on again.

Boiler went through some kind of start-up cycle, after which it started to pump warm water through the radiator supply pipe. Thermostat cut off at ~30 degrees, then ran cold. It re-ignited and pumped water up to 35 degrees, then switched off and ran cold again. Then reignited and pumped hot water to the rads up to ~65 degrees before switching of. It's now heating rad water up to ~71 degrees, switching off until the display cools down to ~40 before re-igniting. This all sounds like a warm-up phase so may be ok. However I would have thought in normal operation the swing from cutting out at 70-ish degrees hot and cutting in at 40-ish degress was a bit much.

When I check the fault code history I get the following:

1. nnn
2. F11
3. F22
4. nnn
5. F1
6. F11
7. F1
8. F1
9. F0
10. F1

nnn = Dont know what this means - guessing nothing

F0 = Flow NTC; NTC broken; NTC cable broken; defective conection at NTC; defective connection at electronics.

F1 = Return NTC. NTC broken; NTC cable broken; defective conection at NTC; defective connection at electronics.

F11 = Short circuit - return NTC

F22 = Dry fire protection


So. it's looking like it's a problem with the NTC. However I can't tell when these fault codes were registered so will have to assume that if it's been repaired in the past the list was cleared and these are new.

Questions:

What's an NTC?

If you agree this may be the problem, can I fix this myself (I'm technically capable - just not familiar with boilers)?

Could someone post instructions regarding how to locate and replace the NTC? I wouldn't touch the gas side of things, but water should be ok.

I'm still not sure if the timer may also be a problem as this seems to happen only in the evenings. Thoughts?

Is there anything else I should check?

Many thanks
Rich[/b]

 

[glasgowgas]

whats the boiler system pressure (when cold)?

 

[ColJack]

View media item 13608 View media item 13607 View media item 13609that would be the things middle of first pic, back of second pic, and middle of third pic ( with orange wire to it )... assuming that it's a turbomax.. ( the numbers sound the same.. )

 

[ChrisR]

What's an NTC?

A Negative-Temperature-Coefficient thermister. ie a temperature sensor.

They're about 10kOhms cold and lower when heated. The Vaillant ones don't often fail.

If you agree this may be the problem, can I fix this myself (I'm technically capable - just not familiar with boilers)?

You have to be gas competent to access the one at the top of the main heat exchanger.

 

[Richard2009]

Pressure when cold is just over 1bar - is this enough?

If consensus is the NTC;s tend to be reliable, any other thoughts regading what to look for?

For interest I left it on all day today and it seems to have been find, so I wonder if it's a startup problem. Don't know what would cause that though - timer or some controller?

Many thanks for the feedback
Rich

 

[ColJack]

is your hot water particularly hot when switched on? it might be that the diverter valve is stuck or gets stuck in the hot water position..

 

[Richard2009]

Not especially hot - the temp control dial on the boiler is probably at 80% and the hot water is "acceptably hot". Certainly not "liable to immediately burn" hot.