Potterton Suprima 100 Lock Out - Expansion Vessel

[JLow75]

Hello to all at DIYnot Forums, this is my first registered post, this looks an excellent DIY Forum!.


I have the Dreaded Potterton Suprima Lock-out problem, that has been occurring on a random basis for a good while. I have checked the Thermostat & temp sensor & they seem to function ok, also replaced the Pump. The boiler is fitted with the upgraded Siemens control unit 3 years ago.

The system is a traditional sealed system - configured & wired as 'S' Plan.

I checked the all the wiring long ago to an S plan schematic and it is correct. The system functions fine when working!.

It has an expansion vessel fitted, the boiler started locking-out again & I noticed the pressure in the tank had gone to near zero -

basically my question is would low-pressure cause random boiler lock-out?.
I have re-charged the vessel to just over 1bar (roughly) so will see what happens now.

The system appears to be leaking all the pressure out, where should I start to look? - apart from the obvious Schrader valve on the vessel.

The lock-outs occur totally at random - morning/night/cold system/hot system etc

Any other relevant tips/points welcome.

I am a 20-year time-served Electrical/Electronics engineer, so you can talk technical to me, I am also a vehicle technician - but I'm specialist Electrical - my knowledge of central heating systems, esp modern is very mediocre!

Thank you in advance

Jamie

 

[algas]

check for air in the system & that the pump over run is functioning

 

[JLow75]

Thanks, the system was quite gurgly when operating - as if there is air in the system, after I re-charge the vessel it shuts up. I have bled all the rads

How do I check the pump over-run is functioning correctly? - just the 'screwdriver' test

For the pump to over-run, does it have to be connected straight to the boiler pump terminals?, as mine isn't - it runs to the S-plan junction box

 

[ianmcd]

yes the pump needs to be connected directly to the boiler terminals and with an S plan you will also need to have a by-pass installed before the two motorised valves, the way the over run works is when the call for heat ceases the boiler will send power to the pump to keep it running till the boiler is cool enough hence the reason for a by-pass as the heat has to go somewhere

 

[JLow75]

Well there's one issue then!, my pump isn't wired directly to the boiler, it's wired to the S plan junction box.

there is some additional pipework around by the two motorised valves, upto the boiler pipes so that may be a bypass

 

[ianmcd]

if it is a pipe that joins the flow and return pipes with some sort of restricting valve(commonly just a gate valve ) but may be a proper automatic by-pass then this is indeed the by-pass so you only need to sort the wiring out, it is not unusuall for a boiler to run for many years with the pump wired up wrongly, if you have a bypass it is an easy enough task to wire the pump correctly

 

[JLow75]

Thanks a lot for your help can you upload photos on here? - if so I'll take a pic and
Stick it up.

There is a lot of air in the system now rads are gurgling like mad, there is 1.5 bar of pressure in the expansion vessel - but the pressure gauge on the boiler outlet reads zero!

i think i may have more than one issue here

 

[picasso]

Look for a filling loop normally under the boiler or near the 2 port valves, then you can put some water in the central heating system.

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• picasso
• 10 Oct 2010
• 6

 

[mogget]

Don't forget to let the expansion vessel down to 0.5 - 0.75 bar if you are going to fill to 1 bar.

 

[GuessMan]

If it is a 100 L there is a flow switch on the boiler, it interrupts the air pressure switch , no water no flow no fan proving = lockout. So check the expansion vessel and get a new PRV.

Look in the FAQ for better advise on recharging the expansion vessel.

 

[JLow75]

Great thanks, I think the system needs a good bleed when cold & maybe balance out the radiators too.

Yes there is a filling loop right near the valves, or what looks like.

okay so when cold - let the expansion vessel down to 0.5 bar, use filling valve to fill system upto 1bar on gauge that correct?

 

[mogget]

Yes but when you are measuring the expansion vessel pressure it is important that the water side of the system has no pressure in it at all. So if there is a drain cock, connect a hose and open the drain cock before checking the EXV pressure.

Check the FAQ for a more detailed explanation as GuessMan has said.

 

[JLow75]

Excellent thanks, will do

 

[JLow75]

This is the pipework by the zone valves, I assume this is the filling valve:

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• JLow75
• 7 Feb 2014
• 1

Also I have checked point-to-point continuity & my system is wired identical to this schematic. As you can see the pump is terminated in the junction box & not boiler?:

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• JLow75
• 7 Feb 2014
• 1

 

[45yearsagasman]

The pump may well be connected into the wiring centre, but does it have a live feed directly from the boilers pcb?