Potterton Suprima 70

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Hello everyone

I am trying to work out if my Potterton Suprima 70 is functioning properly. I have hot water and heating, but the boiler is constantly cycling on and off.

The system is as follows:
- it's located in a flat and is a sealed, pressurised system
- there are 9 radiators, most with TRVS, and a wireless master thermostat in the hall set at 17 degrees
- a mixture of microbore and standard pipes
- a replacement PCB was fitted at some stage.

The boiler will run for about 10 minutes when it first comes on, and then goes off for about 2 minutes. After that it comes on for about one minute and then turns off for two, and then repeats this cycle until the flat gets up to temperature.

During the 2-minute periods when the boiler is off, the pump continues to run and the green light on the boiler flashes.

Because I have water and heating the system is obviously working but should I expect the boiler to fire for a longer period rather than constantly going on and off in this way?

Thank you!
 
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Because I have water and heating the system is obviously working but should I expect the boiler to fire for a longer period rather than constantly going on and off in this way?

yes.
 
Because I have water and heating the system is obviously working but should I expect the boiler to fire for a longer period rather than constantly going on and off in this way?

yes.

Thanks. As I have zero skills in this area I suspect this is going to be one for the plumber...I didn't want to call him out only to be told there's nothing wrong with it.
 
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Same problem here!

> Potterton Suprima 70
> Seven normal radiators and three 'towel radiators' (ie, off the HW rather than CH)
> Standard pipes
> Second replacement PCB (newest type) fitted this morning

The normal cycle when both HW and CH demanded is:

> 2 minutes green flashing – no flame
> 25 seconds green with red flashing – starting the boiler
> About three and a half minutes constant green light – flame

The last part of the cycle extended by 40 seconds when I adjusted the tank thermostat up from 60 to 70 celsius for a couple of cycles anyway, before settling back at three and a half mins.

The last part of the cycle also extended while I ran the shower hot for 4 minutes, extending it to six and a half minutes... which is to be expected of course.

I have checked the resistance of the boiler's thermistor (what the manual refers to as the temperature sensor) at 1.4 mega-ohm, which is in the range suggested by the manual's fault-finding flowchart (between 20 kilo-ohm and 4 mega-ohm).

The Grundfos pump appears vibrates gently throughout the cycle (and my rads are hot so assume that means the pump is working just fine).

Is this cycle normal operation? If not, how can I get it sorted? Thanks in advance.

Related posts:
//www.diynot.com/forums/viewtopic.php?t=165880
//www.diynot.com/forums/plumbi...conds-off-4-minutes-house-not-heating.310482/
 
Watch the Potterton Suprima cycle... possibly the finest three minutes in YouTube history :LOL:

http://youtu.be/ynz_aCgyKLA

Yes, this is exactly what mine does, same time and everything. As soon as it went off 23 seconds into the film I knew it would come back at 2.23...

Homecare came out yesterday and swept out the boiler, oiled the fan etc but it actually worked for them, no short cycling for the first time in months. However as of last night it was back to its usual tricks and I am going to call Homecare to ask them to come back as I don't think this can be right. http://miketheboilerman.com/suprima.htm suggests that I may need (another) new PCB. I guess however the next things to have checked are the pump and the thermistor.
 
Even though the PCB was upgraded five years ago, I too saw miketheboilerman's writeup on the Suprima and assumed another new (well, refurbished) PCB would do the trick. Alas no.

The resistance on my thermistor checks out fine, but wondering whether it's the wiring that links it to the PCB. Hmm.
 
Have you tried turning up the pump speed?

It is possible the boiler is working correct and that the pump isn't pumping away quick enough to stop it short cycling.

Remove the pump and check it is clear.

Or other possible is the boiler is over sized for the system.

Daniel.
 
Hi Daniel

Thanks for this. Pump speed is set to 3, so as fast as it will go. Homecare came out again to have a look and the engineer spent an hour with the boiler. The flow/return difference is about 12 degrees, which is good, the pump is clear of blockages, and the zone valves are behaving. He discovered that the bypass route tap was open fully, so that's now been closed down a bit and seems to have helped, plus my balancing the radiators has also made an improvement. (The lockshields were all fully open.)

However, I think you're right about the boiler being oversized. My back-of-an-envelope calculation puts my radiators at about 33000 BTUs whereas I believe this boiler is 70000...
 

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