baxi 80e - HW & CH on-off-on-off etc :(

[jwturpin]

when either the DHW or CH is running after a few minutes of continuous operation, the flame goes out (If it's CH, then the pump continues to operate).
The flame then tries to kick in again, fails, tries again, fails a few more times, then woof, it fires up. Give it another 30 secs and off it goes again, and repeats this over and over.

I'm about to pay through the teeth for a gas fitter plumber to come sort it, but is there anything I can check out or replace myself that could be a simple cause, a thermocouple or something cheap that is a common cause for these symptoms?

I'm quite adept at fiddling with stuff, but dont have a clue what component might be failing. If its gas related, i'll get a qualified person in, but electrics or water, i'm happy to get my toolbox out.

Thanks in advance

 

[Homesafe]

CH thermister

 

[homes]

CH thermister

Possibly but could be OH stat/pump/blockage, but then you're still New

 

[jwturpin]

How would the CH thermister affect the DHW?
and what does OH stand for...
I would thought as the symptoms are the same regardless of whether its the DHW or CH thats on,that its one component that both systems use. Worth Pointing out that when the hot water is running, when the flame manages to stay lit, I get a steady stream of hot water.

Its not a blockage in a water pipe that seems to be the problem, just the flame has an issue with staying lit for more than a few minutes

 

[Gasguru]

'cos it isn't a central heating thermistor...it's the primary flow thermistor, and it's used in both modes of operation.

They often fail leading to cycling on DHW, heating can sometimes still appear to work especially if the temp setting on the front is low.

AFAIR it's a dry pocket type, a simple job and cheap part to replace but there are other reasons the boiler could be playing up.

OH is the overheat thermostat....but if that operates AFAIK a warning LED will show on the front.

How many of the temperature LEDs light up?

You won't pay through the teeth if you find a "no fix no fee" boiler repairer and don't pay for parts not required.

 

[jwturpin]

My mistake...it's a Baxi 80Eco....not an 80e, so no LED's on front other than Power (green), Flame(orange), and Fault(red).

The orange one is coming on intermittently as and when the flame comes on, and I get cyclic HW. When I put the heating on, same happens, flame is cyclic, and slowly but surely, all the radiators will heat up, but it takes ages as the flame is on/off/on/off etc!

As for the acronyms AFAIR and AFIAK....i'm lost....

Bizzarely, my shower this morning at 10am was uninterrupted hot water, my house mates shower at 8am was mostly cold! I guess these thermistors can fail intermittently ?

 

[Gasguru]

As far as I know

Thermistors often fail by going open circuit once a particular temperature is reached. Easy to test.

 

[baxpoti]

CH thermister

Correct answer, well done Newgas!

Although it's correctly known as a 'primary thermistor'

 

[Homesafe]

CH thermister

Correct answer, well done Newgas!

Although it's correctly known as a 'primary thermistor'

Thank you,

Did you see my post on the 130he in the CC Baxi?

It's still leaking behind the DHW hex after I stripped out pump/plate/divertervalve whole etc. ( Not easy ). Is this a problem connection cos I think it was one of the connections that leaked initially, but now it is the only one tho. ( I hope )

 

[jwturpin]

EDIT: scrap what I said below...heating was working fine, now the boiler won't fire up at at all. when I run HW, I can hear the fan & pump starting up, but not followed by the usual WOOF as the flame kicks in. Same for heating. Bugger!!
___________________
So, turns out my PCB was causing the heating to trip out. When boiler eng removed it, there was evidence of charring around some of the plugs and components. New PCB, so far so good.

A scaled up Heat exch unit was causing the problems with my hot water tripping out. screws holding on the manifold were in so tight he's having to come back and drill them out. As it was 9pm at this point, and he didnt have two new screws with him as it's not normally something he has to replace, I have to wait till Friday for the new heat exch unit.

So still got dodgy hot water, but the CH is working just fine

I just assumed as the symptoms of the CH and HW were so similar it was the same fault causing both.

Does £295 for new PCB, new (higher Kw output) heat exch unit, pressure vessel pumping, labour and VAT inc sound a reasonable price??

JT