Potterton Puma (Mind of its own)

[scorpio1977]

Hi all,

Can anybody throw some light onto a little problem please??

I recently moved to a new house where I have a Potterton Puma combi boiler installed. All has been fine up until a few weeks ago.......... For absolutely no reason at all, the boiler will fire up and I will get FULL central heating even though the "constant" and "timed" switch is set to off........With being at work all week, I dont even have the time clock set to come on at various times, in fact I thought it was the clock itself that was a bit faulty so one evening I disconnected it completely but, to no avail.

It will come on, disregarding the temperature setting on the front and even if the thermostatic valves on the rads are set to off, I end up with scorching red hot radiators throughout the house.

I end up having to turn the entire boiler off at the mains, waiting a few hours and then turning it back on.

Any advice you can give would be greatly appreciated - Its not so bad if I'm actually in the house to catch it but, if it does it when I'm not here, my gas bills are going to be astronomical!!!!

Thank you.

 

[weareleeds]

Boiler is thinking you have tap turned on either because the dhw microswitch is faulty or it is adjusted wrong

 

[undercover]

I'd start by thinking what could be making the combi call for heat. You say youve disconnected the clock so prob ruled that out. Could be a faulty programmer.

Do you have a thermostat anywhere in your house. It could be faulty and switching the boiler on.

Another possibility could be a faulty frost stat or pipe stat. If you house has a cellar take a look.

Then i'd start fault finding in the boiler itself.

 

[Agile]

There are only two things which can make the boiler come on when the switch is not selected for CH!

The DHW switch or the frost stat. The first is very likely and the latter most unlikely.

To fault find boilers you need to know or see how they work.

Tony

 

[scorpio1977]

I dont have a thermostat in the house, I was considering adding one but, not as yet.

I'd start by thinking what could be making the combi call for heat. You say youve disconnected the clock so prob ruled that out. Could be a faulty programmer.

Do you have a thermostat anywhere in your house. It could be faulty and switching the boiler on.

Another possibility could be a faulty frost stat or pipe stat. If you house has a cellar take a look.

Then i'd start fault finding in the boiler itself.

 

[scorpio1977]

Would this make the central heating come on though??

Boiler is thinking you have tap turned on either because the dhw microswitch is faulty or it is adjusted wrong

 

[scorpio1977]

Thanks everyone,

Think I may have to give in to it and call an engineer out......sounds just a bit too technical for me.

Was hoping to be able to sort it myself but it may be more cost efficient if someone looks at it who actually knows what they are doing

Thank you for your help.......MUCH appreciated!!

Martin

 

[undercover]

There are only two things which can make the boiler come on when the switch is not selected for CH!

The DHW switch or the frost stat. The first is very likely and the latter most unlikely.

Tony

And how would the DHW switch turn on the heating side, which is happening with this boiler.

 

[Agile]

Ah...

The DHW switch turns on the boiler, usual things like pump and flame, and because the diverter is in the heating position the heat goes to the rads.

So the customer thinks the boiler is on for CH whereas its actually on for hot water!

Tony

 

[scorpio1977]

Can I ask,

What the dhw microswitch is, what it looks like and can it be adjusted by a novice such as myself??

 

[Gasguru]

Start by taking off the white front cover and checking the red LED on the circuit board is OFF when there is NO demand for hot water.
However I normally find sticking flow switches on this boiler have far more dramatic effects (due the the lag of the diverter).

 

[Agile]

Geoff, there is a wide spread of diverter response times between a new one and an aging waxstat.

Most of the boilers we see are aged and as you say the diverter lag will often cause overheating and sometimes steam shooting out of the AAV.

However, a closed AAV and absorbing air at the top of the rads would lessen the apparent effect.

Just two weeks ago I went to one which was showing no overheating problem and the complaint was just the rads heating up.

It turned out to be a badly worn switch with almost 1 mm of wear on one side only.

Tony

 

[ChrisR]

Scorpio - there are many threads here on Puma dhw flowsitches, with pictures, intructions, etc.
Last one I got going in about 1 minute!

 

[scorpio1977]

Hi all,

Forgive me if I'm being totally thick here.......This is my first house and apart from my Father's experience, I'm a complete novice.

I read somewhere that the black switch on the circuit board could be out of adjustment, when I took the cover off the boiler, there was a black "thing" on the circuit board.....I read that the futher turned to the right this thing is, the more likely it is to over-ride things.

I have turned it fully to the left and for that past few days, touch wood (touches head) things seem to be operating normally.

I am totally baffled by this "fault" but, someone did mention a red light and it meaning its heating the water????............does that imply that a switch is faulty somewhere? - I mean, heating water but yet I get SCALDING radiators??

I was hoping this would be an "easy DIY fix" (and a cheap one) but, its sounding more and more like I need to get someone out to it.

We'll see how this "switch adjustment" goes.

Thanks guys



Scorp

 

[Gasguru]

OK lets start again

On the circuit board you will see a red light (arrowed). With the hot tap ON the light should be ON, with the hot tap OFF the light should be OFF. Turn the tap on/off several times and monitor the light to make sure it corresponds.



If the light is ON with the hot tap OFF it is likely the flowswitch is stuck or the microswitch it operates is jammed on. See the arrow below, lower the "control box" down to see the flowswitch assembly.




If the flowswitch or microswicth require replacement have a look in the manual - the microswitch requires setting up.

The "black "thing" on the circuit board" is the heating output control. It is used to match the boiler heating power to your system size. For small flats set it to minimum, 2/3 bed semis probably half way and only on 4 bed detached would you need to have it on maximum (an unlikely scenario). These boiler run much quieter when this is set correctly.