Suprima 30L - Wont fire up Problem - HELP

[DoggiePaws]

I have a Potterton Suprima 30L and its 3 years old. The sympton of the problem is as follows

1. Switch on the Boiler from cold and you can hear the gas pumping in, the water pump is rotating upstairs and fan in side the boiler begins to rotate. Red LED is on and Green LED is on constantly and not flashing.

2. The Boiler fires up and starts operation for approx 10-15 seconds and then switches off i.e. no gas no fire no heating - the water pump is switched off. The thermostat in the lounge is on MAx temp approx 30 degrees. The red LED is on constantly and not flashing. The Green LED is OFF. At any point i dint hear the boiler attempt to fire the electrodes.

3. I press the reset button and hold onto to it for approx 10 secs or longer and the RED LED is on constantly and the green LED flashes - i hear the gas flowing and the water pump rotating. The fan inside the boiler doesnt come on. RElease the reset button adn continue to hear the gas coming in, water pump rotating, no fan rotating and Red LED on constantly and Green LED on Constantly - after 5 secs no gas, no water pump rotating and Green LED extinguish and Red LED stays constantly on.At any point i dint hear the boiler attempt to fire the electrodes.

4. Switch the whole thing off i.e. remove 240V AC from the boiler for approx 30 mins and return and repeat step number one as above. This time the Fan inside the boiler does not come on, you can hear the water pump, and the gas flow but no ignition. After 5 secs approx, you cannot hear the gas flow and the water pump stops rotating. RED led is on constantly and not flashing.

5. Left it alone for 1 day didnt remove it from 240V AC during that period. House is stone cold and switch off boiler and switch back on again. The Boiler comes on for 8 hours and then the above symptons occur again. i.e RED LED on constantly no gas, no water pump activity and no fan rotation inside the boiler. But yet the desired temperature from the Thermostat has not been reached.

I have checked the following:

a) Water PUmp, receives 240V AC and rotates when the supply is present.

b) Temperature Sensor - reads approx 1M room temp and 700K when i put my finger on it. According to previous topics of similar nature from this forum this is suppose to be normal.

c) Resoldered the PCB

d) AC fan inside the rotates when i apply 240V AC on the motor itself.

e) Air pressure switch is constantly open at any point and the terminals connected to the air pressure switch is 240V AC on both terminals. Disconnect the switch from the PCB and the PCB measures 240V AC on the two terminals that connects to the switch - is this normal? i would expect only one terminal to be 240V AC and not both.

I would be grateful if anyone could assist as i think i have checked every thing i that i think i can. I dont think its the gas valve as i can hear the gas and i dont think its the water pump as i see the 240V Ac and see it rotating - however do correct me if i am wrong on anything - your advice will be greatly appreciated.

MAny Thanks in Advance

 

[gavinda]

check your inlet pressure to the boiler (if competent). should be 20mb +-1 mb. if you can (its a doddle) remove the gfas valve and check the gauze filter on the inlet.. ive found these to be full of 'shavings' many times. sadly only discovered after prev engs have changes 3 or 4 pcb's

 

[baxpoti]

1. Switch on the Boiler from cold and you can hear the gas pumping in, the water pump is rotating upstairs and fan in side the boiler begins to rotate

Strange sequence on this Suprima!
'gas pumping in' before the fans up to speed?

 

[DoggiePaws]

Thanks Gavinda, i will give it a go tomorrow and let you know what i find. I can also add that i have not touch the boiler and left it on with the red LED on constantly for approx 4 hours and no activity - i turned the thermostat in the lounge down to approx 18C - just as a habit and i the boiler fired up - The thermostat LED status indicated that the temperature was reach when this happened. The boiler fired up for about one minute and then switched off. I tried switching the thermostat up to 25C - this allowed the thermostat to indicate that the temperature was below the desired setting. I then almost immediately turned the thermostat reading to 18C - allowing the thermostat to indicate - reached temperature. Guess what? I can hear the water pump rotating, gas flowing into the boiler - no fan, no ignition...weired!! I agree with you baxpoti, very strange set of sequence. I am completely lost with this, i only have Gavinda's suggestion to follow. Hope some more sugguestion will follow...again many thanks in advance.

 

[corgiman]

how can you hear trhe gas flowing to the burner?

what are you getting at the outlet point?

 

[DoggiePaws]

Thanks for the response, How can i hear the gas? Out of the times when i did see the bolier fire up i did witness the following sequence in the following order

1. Water Pump rotate
2. Fan rotate
3. Hissing flowing noise (i am assuming this is the gas flowing in)
4. electrodes spark
5. Boiler fire up

Out of the times it didnt fire up the only thing that did not occur from the above is point number 2.

I have measured the coil resistance on the gas valve and it reads 2.5M from the outer teminals and 2M from the center to any of the outer terminals - Is this correct i think i remember reading it wad suppose to be around 4M - yesterday when i measured it - it was 4M

The coil resistance on the AC Fan is 48 Ohms - Is this too low?

Is my assumption wrong and i may not of heard the gas flowing in? or perhaps it is but not enough flow ? IS ther a flow sensor in the gas valve ? is it this that is stopping the boiler from firing up?

I dont have any means of measuring the outlet so i couldnt tell you what it is.

 

[DoggiePaws]

Sorry my mistake

i measured it wrongly

the readings for the gas valve is as follows

3.75K on the outer terminal
2.4K from one of the centre to the outer
1.3K from the other one of the centre to the outer

 

[DoggiePaws]

Gavinda, have checked out the gauze filter and there is no sign of blockage - all is clean. I am unable to measure pressure as i have no instruments to do so. Thanks for the suggestion.

Baxpoti, are you suggesting that the fan should come on before the gas pumps in. Can you tell me that if the resistance of the motor coil is 48 Ohms - is this abit low?

 

[bribhoy]

fan 48 ohms is ok, top to bottom pin on gas valve (from memory) is 4.1Kohms, these two components sound ok, igntion sequence should be (along the lines of) 1. demand on switched live 240Vac, 2.thermistor and potentiometer (knob) demanding heat, 3. air pressure switch checked open circuit (some of these boilers have a water flow switch wired in series with the APS too), 4.fan on, 5. APS makes (and flow switch if fitted), 6. Overheat stat ok (closed circuit), 7. spark ignition, 8. gas valve open, 9. rectification (main burner lit and sensed). I can't lay my hands on them at the moment but the MI should give you a clear indication from the LED colour/flashing rate, where the problem lies (if it has the new PCB - 40L should have I think, then holding the reset button for more than 10secs will also tell if it is ignition or overheat lockout)

 

[DoggiePaws]

Thanks bribhoy

I pressed the reset buyyon for 10 seconds and the red LED flashes - i guess that is informing me that it is an ignition or overheat lockout - so i tried pushing the terminals on the overheat sensor and hey presto the boiler fired up....weired....dont know if its coincidence or not - but there could be an overheat sensor issue. I have someone coming in to look at it on Tuesday so i will let you all know what the outcome is.