Ravenheat RSF 84 - thermistor!?!

[mogsyd]

Hi, my hot water recently went off on my above named combi boiler, I notice the pressure was below 1 bar, so I increased the pressure upto just under 1.5 bar (as instructed in the manual). I then turned on the hot water tap and the boiler fired up then cut out a second or so later. Since then the boiler wont fire up for hot water only for the central heating. I have come to the conclusion it is a possible fault with the thermistor. What i was wondering is, is there a way of testing it to see if its faulty? before i got buying a new one and replacing it.
Or id there any other possible reason for this fault???
Many thanks in adv
Dave

 

[SortedPlumbing]

Thermistor wouldnt stop it from lighting. if it was thermistor it would light up then shut off.

Possible fault on that boiler is fan which i have had before - heatin worked fine but fan wouldn't go to full speed when calling for hot water.

 

[mogsyd]

thanks SortedPlumbing, is it safe to take the front panel off and turn on the system to check the fan?

 

[SortedPlumbing]

To check fan you would need to break chamber seals,
so if ur not corgi i wouldnt!

Does the boiler not even try to fire on HW?

 

[tonybhoy]

No,but it won't do you any good anyway because the boiler will fire with the casing off,which is very dangerous.

 

[mogsyd]

To check fan you would need to break chamber seals,
so if ur not corgi i wouldnt!

Does the boiler not even try to fire on HW?

its did when i first increased the pressure in the system, now it doesnt fire up at all for DHW
still works for CH

 

[SortedPlumbing]

1st thing i would look at on ur boiler is fan/flue.

 

[mogsyd]

just so i get this right. when the hot water tap is opened and the water begins too flow through the boiler what triggers the boiler to ignite? is it the thermistor or something else.
i presume the CH works the same way but the thermostat triggers the flow of the water and the thermistor triggers the boiler to ignite
correct me if im wrong :S

 

[tonybhoy]

just so i get this right. when the hot water tap is opened and the water begins too flow through the boiler what triggers the boiler to ignite? is it the thermistor or something else.
i presume the CH works the same way but the thermostat triggers the flow of the water and the thermistor triggers the boiler to ignite
correct me if im wrong :S

Depends on the boiler but usually a microswitch starts the whole thing or the pcb does.

pump/fan/aps/gas valve/burner.

Thermistor only monitors flow and water temp for the PCB to decide how and where the boiler delivers the heat.

 

[mogsyd]

right just had another read of the manual and looked at all the switches. There is one called the DHW pressure switch. upon closer inspection i seen the switch isnt being pressed by the 'paddle' (if thats what u call it'). any ideas? i presume this switch should be pressed in as the flow of the water increases?

 

[SortedPlumbing]

try and make that switch manually. - if boiler fires up when you make that switch then its ur diapharm

 

[mogsyd]

it does fire up manually when i press the switch. is a diapharm expensive and easy to replace?

 

[mogsyd]

anyone have any thoughts on this? (see above post)
thanks

 

[SortedPlumbing]

Its fairly easy to change. not sure how much it costs.......and im sure it tells you step by step how to change it in the manual!

 

[mogsyd]

this boiler is crazy.
right just turned the CH on, lights up ok, so i turn the hot water on, still burning, then i turn the CH off and the boiler is still burning. So then i stop the DHW and the boiler goes of, I leave it for a bit then turn the DHW on again and it burns up fine. :S
absolute madness?!?!?
gonna leave it for a while then see if it lights again with just the DHW, fingers crossed ey