Potterton Puma 100 permanant pilot DHW too hot

[macpepper]

Hi there, can anyone help? The DHW on this boiler is too hot! I have followed the diagnostic flowchart and replaced the Hot water temperature sensor and the hot water overheat thermostat, but to no avail and I seem to be going around in circles! If I disconnect the wires to the modulator solenoid G3, the flames and temp drop as per diagnostics.

Thanks in anticipation,

Mac

 

[gas4you]

Firstly you need to check the flow rate of water through the boiler. Does the tap run slower of late? The slower the water the hotter it will get.

If water flow is too low I would suspect the plate heat exchanger scaled up.

When ch is on can you see flame modulating down? If not could be fault with gas valve.

 

[macpepper]

Thanks for your kind reply Dave. The exchanger was replaced about 4/5 years ago because of scaling and a proper water softener was installed at the same time. I perhaps wrongly assumed that this would prevent scaling in future.

Thanks again for your help.
Mac

 

[gas4you]

Do you mean a 'proper water softener with salt', or a scale inhibitor just for the boiler?

If you have the water softener working correctly all the time then it should prevent further scaling. If it is an inline inhibitor then other than ones that you replace the cartidge or chemicals annually then my opinion is that they are a waste of time and money

As said check to see if boiler is modulating down.

 

[macpepper]

Sorry Dave - yes ch is modulating down(the flame drops as I turn down the CH nob - is that what you mean?) , and it is a proper water softener with salt ....

 

[gas4you]

Well you should have no scale problems then. When was it last serviced?

 

[macpepper]

Can't remember exactly - probably 18 months ago. When the DHW is on and I turn down the temp nob on the panel, the flame drops for a second then goes full bore again, unlike the ch, where I turn nob down and flame stays low.

 

[gas4you]

Not knowing these boilers inside out I can only think that if there are no problems with water flow then one must suspect the modulation board is at fault, unfortunateky this retails at around £130 + VAT.

 

[macpepper]

Thanks Dave, will let you know outcome...cheers

 

[Baxmax]

If water flow is too low I would suspect the plate heat exchanger scaled up

Wheres that then .

 

[Agile]

The first thing to check in this situation is that the water flow rate is correct.

The second thing to check is that the gas valve is set up correctly. That needs a competent CORGI.

A competent DIYer could set the flow rate to 9.3 li/min and check the gas consumption at the gas meter.

Tony