Bosch WMTC3300 Dryer

[Dober_paw]

I have an 11 yr old Bosch Nexxt WMTC3300US/01 dryer – that isn’t heating.  Some  history – over the last couple of years it has popped the Hi-Limit protector a few times – and I finally replaced it last year.  It stopped heating last week – not the Hi-Limit this time  . . .  Checked the heater coil – it has continuity.  Checked all the duct work - clear.   I decided to replace the NTC at the heater  00163297 (AP2805409).  Put it in, turned dryer on –and I could see the heater coil warm up and hot air came out. So I put the back on, buttoned it up and called it job done.   Started a load, but, within minutes it was no longer producing heat.    Decided to replace the NTC at the lint catcher   Bosch #00154166.   Put it in, turned dryer on – and no heat.   In frustration I flipped through several of the dryer settings hitting ‘start’ at each – somewhere in there it did produce heat, but not repeatable/consistent.    

Putting it into ‘test’  mode does not show any error codes (in ‘view fault codes’ position – the LED display is blank). Not entirely sure what the other tests are meant to do/show - but none give an ‘error’ message.

I’m now eyeing the heater relay with suspicion.  With the dryer running – the hi-voltage contacts are open . . . but is that because there’s a fault in the relay, or is it because one of the sensors has decided to stop calling for heat?  How do I test for presence of signal on the solenoid contacts?    

What else should I check/change ?

Thanks.
Dober_paw