Potterton Suprima 50L Flashing Green Light

AtariMark · 8 Jan 2010

I have a Potterton Suprima 50L that is 10 years old. I fitted a new PCB in May 08 to get rid of the known lock out issue caused by dodgy a PCB and it worked fine until a few weeks ago. I replaced the PCB again today and the fault has not gone away.

The problem shows itself up when the central heating is on. The boiler starts its sequence: fan on, gas lights and burns for 5 seconds then boiler stops with a flashing green light which means the boiler thinks it is up to temperature. I have changed the thermister but the problem is still there. I measured the resistance of the thermister and it matches the value Potterton say it should be.

If I run some hot water off, the cylinder stat operates so there is a demand for heat from the boiler. The boiler fires up fine and stays on until the water is up to temperature. Because the timer is still set for central heating and hot water, the mid position diverter valve lets the hot water from the boiler into both the cylinder and radiators so I get a warm house.

The PCB kit comes with all new cables including the one to the spark thingy.

Any ideas how to fix this as I can't keep having showers or running water off?

gas4you · 8 Jan 2010

Nothing to do with the boiler.

Sounds like the 3 port valve head is at fault.

AtariMark · 8 Jan 2010

I thought the boiler would have stayed on if I took the thermister out of it's housing as it would only read the temperature of the air. I had a look at the valves and they look like they are working but I probably need to investigate a bit more.

MANDATE · 8 Jan 2010

agree with gas4you. Most likely the actuator is not moving the valve to the to CH only position, or if it is then micro switch faulty which prevents boiler from lighting.
This microswitch is not involved in lighting boiler when HW is involved. Boiler relies on powr from cylinder stat.
Best solution is to replace actuator head

ScottCheg · 8 Jan 2010

gas4you said:
Nothing to do with the boiler.

Sounds like the 3 port valve head is at fault.

Nail...head. G4Y has hit it.

Scot.

AtariMark · 9 Jan 2010

I have 2 * 2 port zone valves. The CH one is a Myson MPE222. I could not make it to the plumber supplies before they shut at midday today. The actuator moves fine so I took it off but I cannot get into it cos of the stupid security screws. So I put it back on and tested what voltages I got when the CH or DHW was turned on. In both cases I got some strange results, the Myson has connections to the motor which are all correct. The microswitch has three wires going to it;

1) Switched Live to the boiler (Orange)
2) Permanent live (Grey)
3) Make safe (white) - not connected

Normally the Switched live to the boiler is connected to the make safe and when the switch operates, it connects the switched live to the permanent live.

Clear so far? Right I tried this with the CH off and ON and I get ~100 volts on the switched live to the boiler which does not sound right. I would have expected 240v to go to the switched live.

Any ideas? I will disconnected both valves and see what happens later today.

nickso · 9 Jan 2010

put 240v into boiler switched live and see what happens. if it still plays up with a seperate 240v SWL then its the pcb.

i know you say you replaced it but a suprima sitting on a flashing green when heat is demanded means it thinks its up to temp. often they fire up every 10 mins or so for 30-40 seconds and go back to flashing green. ive had one do this out of the box but otherwise its an uncommon problem. thermistors almost never go faulty on these, dont remember ever replacing one.

MPE222 or 322 valves are unreliable ****e.

AtariMark · 9 Jan 2010

OK I have disconnected the switched live out of the valve and measured the output, I am only getting 35v AC when the valve has moved so it looked like it is faulty. To be sure, I disconnected the wiring from the DHW valve and I know there is demand to heat up the water but I am only getting 9v AC on the switched live from the DHQ valve.

Before I go blowing up my PCB, can someone else confirm the switched live output from the valve should be 240v?

nickso · 9 Jan 2010

AtariMark · 9 Jan 2010

nickso said:
yes

Ok done that and my CH has now come on so I have left the link between the two on for now. Just need to get a new actuator, looked locally and they are very expensive so it may be an Internet order.

nickso · 10 Jan 2010

AtariMark said:
nickso said:

yes

Click to expand...

Ok done that and my CH has now come on so I have left the link between the two on for now. Just need to get a new actuator, looked locally and they are very expensive so it may be an Internet order.

take the plunge and order a complete honeywell or perhaps an ACL. the myson junk rarely lasts much more than a year.

diynot

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Potterton Suprima 50L Flashing Green Light

ScottCheg

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