heating works fine,hot water runs and then the boiler starts pulsating,pressure guage goes mental and burner cuts out.relights and does the same cycle all over again.had the same problem a year ago and changed diverter valve head and pcb,problem eventually cleared but not because of new parts as it took a while after fitting to clear.i'm thinking heat exchanger scaling???would really appreciate any help,thanks in advance,kev.
potterton puma 80,hot water problem
- Thread starter kev111162
- Start date
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many thanks for the reply,this morning i took the flow switch apart,rubber diaphram in perfect condition,mechanism free moving.oiled them any way,put swich back together,checked microswitch operation with tap runnig on and off and every thing seems fine,boiler still has same fault.light goes out when tap turned off?????
I had thought that you may have not described the symptoms properly as they are typical of the DHW flow switch except that they occur when the DHW is turned off and its an easy problem to solve.
DURING DHW the pump should run to circulate system water around the heat exchanger. However even if it does not run the boiler will still produce DHW quietly!
The first thing to check is the resistance of both heat sensors cold. Should be about 10-13k.
If they are both OK then it sounds as if the heat exchanger is badly sludged up on the system side
Tony
DURING DHW the pump should run to circulate system water around the heat exchanger. However even if it does not run the boiler will still produce DHW quietly!
The first thing to check is the resistance of both heat sensors cold. Should be about 10-13k.
If they are both OK then it sounds as if the heat exchanger is badly sludged up on the system side
Tony
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once again thanks for replies.the hot water flow rate ia approx 8 litres per minute but the temp rise is small because the cycling keeps coming and the burner has to relight.when burning the flame keeps constant until the shuddering and then goes out.if i vary the temp knob it does seem to modulate the flame.if it is scale am i right in thinking fernox or sentinal wont be any good on hot water side if i try putting that in.cheers kev.
If they are both OK then it sounds as if the heat exchanger is badly sludged up on the system side and i would aim to treat that in situ with chemicals.
It would be extremely rare to scale on the DHW side on your model and even then the boiler would quietly modulate back.
Nothing more I can suggest until you have measured the resistance of the sensors!
Tony
It would be extremely rare to scale on the DHW side on your model and even then the boiler would quietly modulate back.
Nothing more I can suggest until you have measured the resistance of the sensors!
Tony
thanks again.the resistance of hw sensor is 13.8kohms,the ch sensor is 8.8kohms with the appliance in an used cold state.if the system is scaled up do you mean on the ch side and would x200 help???if its the ch system scaled up why does the ch work ok???
Although you have answered the questions we have asked and seem to have described whats happening there is no obvious cause for what you have described as the fault.
This boiler is rather odd in its design but apart from a small number of common faults which occur too often its actual reliability in other respects is quite good.
I cannot come to any conclusion from what you have said so far although if I was there I am sure I would immediately find the problem.
You really need 50g of citric acid which you can buy as Fernox DS40 dissolved in 100 cc of warm water.
Close the system isolating valves ( they may leak and have to be replaced ) and drain 200 cc of water from the boiler. Remove the AAV and pour the DS40 solution into the AAV tube and then replace the AAV.
Repressurise the boiler by opening one system valve a tiny amount until its about 1.2 Bar and then use it for DHW for an hour or two. Then drain the boiler only and repeat the DS40.
If its coming out very black and green then repeat a third time and then just top up with plain water.
As you do this you wil get an idea of any improvement and that will give a clue how many more times you might have to repeat it.
As I said at the start this may NOT be the cure but its well worth trying it. There is always the possibility it will cause a problem if parts of your boiler are corroded so you do it at your own risk!
Lets us know what result it gives.
Tony
This boiler is rather odd in its design but apart from a small number of common faults which occur too often its actual reliability in other respects is quite good.
I cannot come to any conclusion from what you have said so far although if I was there I am sure I would immediately find the problem.
You really need 50g of citric acid which you can buy as Fernox DS40 dissolved in 100 cc of warm water.
Close the system isolating valves ( they may leak and have to be replaced ) and drain 200 cc of water from the boiler. Remove the AAV and pour the DS40 solution into the AAV tube and then replace the AAV.
Repressurise the boiler by opening one system valve a tiny amount until its about 1.2 Bar and then use it for DHW for an hour or two. Then drain the boiler only and repeat the DS40.
If its coming out very black and green then repeat a third time and then just top up with plain water.
As you do this you wil get an idea of any improvement and that will give a clue how many more times you might have to repeat it.
As I said at the start this may NOT be the cure but its well worth trying it. There is always the possibility it will cause a problem if parts of your boiler are corroded so you do it at your own risk!
Lets us know what result it gives.
Tony
J
jonseyrs
Come across this on a few puma boilers, found to be the dhw flow switch every time.
kev111162 said:
Your assuming, he meant the 'red LED'
OP, how often do you have to buy a new kettle?
Do they scale up quickly (within 6 months)?
Your temp sensor readings are within tolerance
For your info the readings are
at
10ºC 20k
20°C 13k
30°C 8.0k
40°C 5.3k
50°C 3.6k
60°C 2.5k
70°C 1.8k
80°C 1.3k
90°C 0.9k
100°C 0.7k
Which PCB did you have replaced last year? FSC or MOD
thanks guys,it's the perm pilot version and i replaced the modulation control board.the red light i am watching is on that board and lights as soon as i turn on the hot tap and goes off when turn the tap off.one other thing i have discovered is if i pull off one the wires on gv3 modulating gas valve the boiler does not fault but the water temp is only warm,just about warm enough for a shower but not hot enough to wash up,it does however stop the horrible pusing of the boiler.
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