Ravenheat HE85T combi boiler issues

ksareen · Jul 16, 2010

Hi, Ive a query regarding 4 year old Ravenheat HE85T combi boiler, this is very similar to CSI85T for those who know this boiler.

The boiler has had new CH and DHW thermistors 2 or 3 times during its life so far along with ignition PCBs replaced 3 times.

The boiler is currently giving issues running the DHW, with or without CH. The boiler fails to sense demand for DHW when tap is opened and does not fire OR fires once and then goes off, but then does not come back on again. The DHW thermistor is wet pocket type and gets corroded/ scaled every year. The CH thermistor is clip on type and much more stable.

I disconnected the DHW thermistor and connected a new one. DHW runs fine but only for a few days before it goes back to the problem explained above. I've thrown another new DHW thermistor today and its running fine now but I've a feeling its going to go wrong again.

Any ideas?

Thanks..

aggis · Jul 16, 2010

Presume the dhw flow switch is working, pump on, if boiler fires briefly does only the flow side of the water/water heat exch get very hot, if so it's blocked.If you have a spare dhw ntc. disconnect leads & fit to spare just when blr shut down. if boiler then fires up, it's def the w/w heat exch.
When turning dhw on If pump not on check dhw micro switch.
Have had a R/heat boiler with a faulty overheat that intermitantly turns the boiler off prematurely on dhw.
Check ntc resistance think it should be 10 -13 k/ohms cold, reducing when hot.
After all these could be pcb, but would ring R/heat technical 1st
Good luck

Billy Bob Bob · Jul 16, 2010

i had this fault on a csi85t it was the ch thermister

wnjswozo · Jul 16, 2010

save your money on call outs,repairs.bite the bullet and get a decent boiler fitted.

Mbear · Jul 17, 2010

Where I live/work the water is soft so I've never worked with any hard water or calcium filters or anything like that and having never used them I don't know anything about them. Surely a filter on the incoming mains would be a good investment and save u cash on replacing boiler parts.

Prevention is better than cure.

Ps next time u buy a boiler, don't buy it from b&q.