Potterton Puma 80e - DHW causes lockout after 2 - 4 minutes

[Matt - cold showers]

We have recently bought our first house and the Potterton Puma 80e (i know, i've read the posts - i'd replace it if i could afford to) has caused a few problems... I have had it looked at by British Gas Homecare, they fixed the central heating problems by doing something with the pump, and changing the PCB. However the DHW problem remains.

Basically, when running the HW after 2 - 4 minutes the flame light goes out and the lockout light comes on, if i press reset it relights, then 2 - 4 minutes later it repeats the problem, and so on.

British Gas have said to fix this they need to replace the Heat Exchanger as it is scaled up, which seems fair enough, we are in a hot water area and the house was unoccupied for a while with a dripping tap.

My questions are;

1 - can the heat exchanger be cleaned/descaled without replacing it?

2 - would turning down the mains water pressure help, my stopcock is fully open and the pressure is good

and

3 - can something be fitted to the boilers water in pipe to stop limescale or even reduce exisiting limescale in the system

 

[cross thread]

you can get in line scale reducers, but secondry heat ex best replaced

 

[baxpoti]

but secondry heat ex best replaced

Learnt something there, I didn't know Pumas had secondary heat ex

First check the diaphragm and microswitch operate correcttly, check the gas valve is modulating, then...........

 

[pannierstan]

but secondry heat ex best replaced

Learnt something there, I didn't know Pumas had secondary heat ex

First check the diaphragm and microswitch operate correctly, check the gas valve is modulating, then...........

You are quiet right Baxpoti it doesn't!
Now now Gordon don't go confusing things

How hot is the hot water during this 4 min period?? Cold/warm/scalding?

 

[pannierstan]

you can get in line scale reducers, but secondry heat ex best replaced

A scale reducer wont get rid of whats already there

 

[Matt - cold showers]

Thanks for the replys

The water starts off at the 'right' temperature, and stays at the temperature until about 20 seconds before the lockout, when it gets warmer, but not excessively so.

This comment in the manual made me think the Heat Exchanger could be cleaned rather than replaced

'5. The heat exchanger waterways can now be descaled or a replacement heat exchanger can be fitted, in which case the overheat thermostat must be transferred to the new heat exchanger'

 

[ChrisR]

Yes it can be descaled, but if they're saying:

British Gas have said to fix this they need to replace the Heat Exchanger as it is scaled up,

and it's covered, then fine-
If not then descale it. If you watch the flames while the HW is on, do they visibly "turn down" from what they are when everything's cold?

If you have hot and cold feeds to the washing machine you can probably descale it yourself with a little ingenuity.

we are in a hot water area

Oooh, there's handy. Thermal springs?

 

[Agile]

"""we are in a hot water area and the house was unoccupied for a while with a dripping tap."""

You must be in Iceland or NZ if you have piped geothermal hot water to your property, not Kent !

 

[Matt - cold showers]

Well, obviously I meant 'hard' water and not 'hot' water, although the attraction of Icelandic Geothermal energy isn't lost on me as the shower went cold again this morning!

I do have hot and cold water feeds to the washing machine... perhaps a clue to being ingenius???

 

[ChrisR]

There are are 2 places different scales can be a problem. One each side of the heat exchanger. One side (primary) is boiler water, the other tap water.
Primary side needs chemical in the boiler water, secondary you can do via the WM hoses, with a pump of some sort and a descaler. Know one chap who does secondary with a pump-up garden sprayer. Pump the jizzm through and into a bucket, and repeat.
Primary side gets its grot from rusting rads - do a search on sludge, and on powerflushing.
Pumas don't usually suffer too much with scale in the primary side, and in your circs I'd try the secondary side first. Use Fernox DS-3 (sulphamic acid).

I'm not in a hard water area so don't know if the water flow would be affected by limescale buildup. Breezer had this problem - he might know.

 

[weargas]

Pump the jizzm through and into a bucket

I don't suppose you have the chemical symbol for jizzm do you Chris? I can't find it anywhere on the internet. I looked but all I came across (oo-err missus) were sites that wanted to charge me a fortune for pumping jizzm into a bucket (one of the buckets was called Angela, she was from Russia and didn't look much like a heating engineer)

 

[breezer]

Breezer had this problem - he might know.

I cant see how I can help

I will tell you all i do know (if it helps or not / any q's ask)

We have the potty puma 100e
Dont know how old it was when similar problem (lock out light) started.
It couldnt have been 5 years old though.

It had a new hx on 19 / 11/ 02

it seemd to work for a while, then it stated again (lock out light)

in 11 /04 it had a new gas valve (and all its "extras")

(no idea why that ws changed, probaly becuse it was "locking out again"

I cant find the "invoice" but i do know it also has had a new pump (the old ones impellar was all smashed) I was bringing in the BG bloke a cuppa as he took it out.

I think it still decided to lock out after all this.

one day a new (new to us) bg bloke came saying he had spoken to his mate and he had heard about our problem and he was going to fix it.

he spoke to his mate on the phone to confirm what his mate said and wher the bit he needed is and hey presto, he didnt have one, but came back next day and changed it. (but i cant find the "invoice" for the date)

over all i think that nice that they were, most of the bg guys were fixing the problem not the cause.

I cant find the h/x i think mrs Breezer has binned it

I am of the opinion it never was a scled up h/x but the little bit all along.

I suggest you ask bg to change the little bit FIRST (since a new h/x cost us £360) and the little bit is "free"

When i say invoice the only thing we actualy paid for was the h/x but each time they came they left us an invoice with a cost of £00.00

the little bit goes by the name of

"this thing 'ere mate"

so if you ask them to change "this thing 'ere mate" you will be alright

Sorry, i thought that funny.

It was the overheat stat, aparently the bloke on the phone said its quite common and does make you think its something else (or words similar)

good luck

 

[baxpoti]

Some Puma facts that may assist

1. If its scaled up, its normally very noisy, its overheating/kettling
2.Lockout indicates a flame failure, a faulty thermistor, an overheat stat opening or a fault with flame sensing.
3.Thermistors are identical wet pocket NTC resistor sensors
resistance at room temp less than 15ohms
4.Does the fan and/or pump stop or keep running after lock-out occurs
If only the fan stops its the dhw o/h stat Operates at 75* and needs to drop below 65*
If both fan and pump stop its the c/h o/h stat set at 97*

Hope this helps