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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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Potterton Suprima 100 boiler. Erratic function: sometimes comes

Resolved Question:

Potterton Suprima 100 boiler. Erratic function: sometimes comes on as per timer instruction, sometimes not. Will open the motorised valve for CH or HW but not both at same time. So the valves are working, the thermostats for HW tank and the wall thermostat for CH all seem sound as can get them to function if turn the whole system off at mains, then 'reboot'. Few days ago, replaced the PCB, as the whole situation seemed so bizarre, could only be the electronics. Sure enough, there were loose joints round 2 zener diodes on the board. Worked perfectly the day after, now back to old tricks, but maybe not as bad. Before PCB replacement, [reconditioned PCB] would often go into 'lock-out'. Now when dormant and not responding to call for heat, the red light is on, but not flashing as for lock-out. Opened the cover when replacing the PCB, and note some gravelly material. One thermistor? [a little electrode covered with white material] was loose. Replaced into the hole on the exiting water pipe. The other thing I notice is that boiler seems unresponsive to the max heat setting [black knob with scale from 1 to max] on the control panel. So seems to have long periods of flame burn. Pump seems OK and set to second speed.

Baffled! Suggestions?
Submitted: 5 years ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 5 years ago.
Hi my name is XXXXX XXXXX lets see if we can get you sorted in the shortest possible time. You sound like you are still having problems with the PCB. Normally the only way is to replace it with the genuine PCB kit (Parts Center part number 424146) which include a rewiring kit. It will clear any fault from the boiler - locking out for no reason, not firing when it should. It is the programmer that opens the motorised valves, and the valves that turn on the boiler. Please make sure the valves always open before looking at the boiler.
Customer: replied 5 years ago.

Here is what happens: if the first call for heat was from say HW, valve is opening, boiler is coming on and cycling until pre-set temperature is reached. While in this state, CH call for heat is ignored. If call for heat was first from CH, rather than HW, the opposite happens i.e. the system services the CH side and the HW is ignored. The system has been servicing the HW side for the last few hours, but CH ignored. I just went to programmer, advanced the unit so that HW is off. Advanced CH to on, you can hear a relay click and CH valve opened. Boiler fires up.

So now believe the problem is and probably always has been the programmer, not the PCB? Would explain why the whole system often did not do anything first thing in the morning, or only did one thing, in a random pattern. It feels like the programmer has some sort of internal fault which is not sending the motorised valve a signal to open if it already is "busy" with the other circuit. As the new part you recommend is variously between £180 and more [Part Centre want nearly £300!], can the programmer be bought seperately? The boiler serial looks like AHHV942 0078 with another code being(NNN) NNN-NNNN If below a certain serial number, the fan needs replacing as well...............

On a seperate issue, there is a bypass back to the boiler between pump and the 2 motorised valves. One part of me says leave it open to avoid overheating, the other says close it to speed up the HW or CH response and save water needlessly cycling between pump & boiler. Have read I should maybe 'balance' the bypass. That's the last question, thanks.
Expert:  Andrew Smith replied 5 years ago.
Stay away from a boiler fault at the moment. You only need a bypass if there is a pump overrun (does the pump stay on once the boiler is turned off at the timeclock?). Can you get the make and model from the programmer? It could be a faulty switch inside the programmer?
Customer: replied 5 years ago.
There is a pump overrun. Will have to open boiler to get make and model of programmer. Will come back with this info.
Expert:  Andrew Smith replied 5 years ago.
The programmer is on the boiler and not on the wall? The pump overrun can be sorted by closing the valve and then only opening it one full turn.
Customer: replied 5 years ago.
The programmer is in the boiler. I prised it out of control panel. It is grey plastic and square in shape. Digital LCD display. 6 small black buttons, 2 red lights for HW/CH. Programmable to 2 steps [on or off]for each channel per day, but not programmable for days of the week/weekend. About 2" x 2" at the back. There are 5 wires: two are the [220V AC?] power supply and there are 3 other wires, one of which is yellow, one brown and one crimson. Held by 4 lugs or clips. It is a BP2000 model. It also says ener-tech electrics but I know this was a specialist company that made stuff specifically for Potterton.

Would imagine this is a standard shape of controller and could get something that would fit? Have you seen similar made by say Honeywell?

Thanks for the info on the bypass - exactly what I thought.
Expert:  Andrew Smith replied 5 years ago.
I found this in the manual. You should speak to your local parts center;

Customer: replied 5 years ago.
"I found this in the manual"

I assume you found the programmer as a separate part in the manual?
If you can see a part number of any kind, please let me know.

In which case this is all I need - thanks.
Expert:  Andrew Smith replied 5 years ago.
All it says is SUPKITH - Try Parts Center in the morning.
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