No heating and no hot water

[mick33]

Hi there in need of some help

I have a potterton prima30f gas boiler and have come home tonight to no hot water or heating. I have looked to check that the timer and stats are all set correctly and that there are no obvious leaks. The expansion tank is full. The pump runs and the boiler is firing and staying alight

I have selected each system individually ie. the water to be on and the boiler will light and pump run but nothing will heat up. I have tried bleeding but to no avail. and also heating with the same results.

The motor on the three way valve moves and and moves accordingly depending on what is switch on

All the pipes leading to the boiler and away from remain cold

Am i right in thinking that if water was not flowing around the system the boiler would keep on cutting out? The boiler stays running

Help would be greatly appricieated
mick33

 

[ChrisR]

Check the pump is working. Search on "pump" to see how. It seems it isn't so check its power supply.

 

[mick33]

hi thanks for the reply, very rapid response.

I have checked the pump by removing the front screw and the pump is running. I have also checked out the wiring for the pump, 3 way valve and controller but still no joy.

I cheated the system by switchhing on the imersion over night and then getting the pump to run with the 3 way valve selected to manual, rads became warm, proving the pump runs

I'm beginning to suspect the fault is with the boiler, maybe with the main burner. I can see the pilot light but i'm not hearing the whoomph and the boiler is cold to touch after an hour as are all inlet and outlet pipes.

Am i right in thinking that with the pilot light lit that the electronic controller runs the pump as its expecting the burner to fire up and the noise i can actually hear from the boiler is in fact the fan running?

Sorry if i sound like a complete muppet i know a little but not a lot

 

[kevplumb]

sounds to me like the 3 way valve is iffy

 

[ChrisR]

Wake up Kev his pilot's lighting!

I assume the pilot and fan both stay on.

Wot happens next is that the pcb looks to detect that the pilot has lit. If it sees it, the sparking which lit the pilot stops and the pcb applies power to the gas valve to open the main burner.

Does the sparking stop?

If it doesn't then the flame detection bits aren't working. Could be the pcb but more likely the pilot is too poor a flame for it to be detected. A corgiwallah will clean the pilot bits and make sure flame is in the right place etc.

If it DOES stop then you'd check that the right voltage is coming from the pcb (pins T1 and T3 mains), and getting to the gas valve.

You should hear the gas valve open with a clunk.

If no voltage then check gas valve coil for continuity/short - should be a few kOhms.

If the coil is open circuit it can possibly be replaced without the whole valve.

If no volts then pcb dead - I have plenty!
If you have volts and no clunk you can check for magnetic field at coil ...a bit tricky.
If you have volts and clunk noise then you need a new gas valve - not someting you'd change yourself.


Any bets, chaps? My 10p's on a dirty pilot injector.

 

[mick33]

Chris R many thanks have done as you suggested.

I have now got to this situation where the main burner will light but will cut off after a short while. Does this sound like the boiler thermostat? i'm not having to reset any overheat thermostat but i'm stumpeed now for ideas.

mick33

 

[ChrisR]

How long is short and how hot is hot?
COuld just be the pilot being pulled about by the main burner - typical if it has grot in it. It'll need the gas pressure checking too so get a corgi in.

 

[kevplumb]

must remember to leave the bottle downstairs before posting

 

[mick33]

Chris R thanks for this help

The main burner will run for varying lenghts of time, from 30 secs to full burn upto room temperature. It seems the hotter the boiler becomes the harder it becomes to relight.
Sometimes when the boiler reaches the room stat setting, it will relight when the room temp drops, other times it doesn't.
Am fast running out of ideas

 

[kevplumb]

firstly apologies for downing a bottle of southern comfort and expecting my brain to work
when the boiler wont light hot is it going through the ignition sequence?

 

[mick33]

kevplumb

Hi yes when trying to light it tries to go through the ignition sequence and the pilot light will light spark goes off and burner will relight then go out straight away.

 

[kevplumb]

would suspect fan pressure switch it sounds like the control dont know the fan is running so ****s down

 

[ChrisR]

If you can check T4 on the pcb module that's the return from the air pressure switch. It should stay at 230V ish all the time the fan's running.
T2 is a neutral - as is the blue wire.

Can I increase my bet on it being pilot flame to 15p?