Potterton Puma 80 CH Problem

[FarmerJohn]

Hi,

Although the hot water works fine I have a strange problem with the CH which has gradually got worse.

I have tried several attempts at fixing this problem and yesterday even replaced the pump which has not corrected the problem. I realised after some thought about the matter that perhaps I am looking in the wrong areas.

The problem is that when the CH is switched on to constant the pump starts the boiler fires up and hot water is driven out the system all as expected. After about a minute the boiler switches off and then some time later it switches back on for a while and then back off. This cycle repeats.

For a completely cold system I would have expected the boiler to have stayed on until there was hot water being returned to the combi. In other words until the radiators had warmed up. This is not happening. In fact I am only able to fully warm a single radiator the way the system is at the moment.

I checked another combi this morning and found that the boilder did in fact remain fired until there was a hot water return and then it would operate as required to keep the radiators warm.

Can anyone tell me the most probable cause of this behaviour and what I need to resolve the problem?

FarmerJo

 

[gavinda]

sounds like a circu;lation issue.... could be simply the three port, could be more. comparing it to another boiler wont help unless its the same model.

have you done any ting to the system lateleyt, bled rads etc. check your boilers pressure too. should be 1-1.5 bar on the gauge when cold.

 

[bengasman]

lack of maintenance has killed the diverter

 

[FarmerJohn]

How can I test the diverter? Is it possible that the diverter is stuck in the how water position but allowing some radiator flow?

Is the diverter the valve with two yellow wires going to it in behind the control panel?

 

[Gasguru]

The diverter valve is a purely mechanical device...it operates by wax expanding in volume.

The slightest drip from a hot tap or water leak can prevent the diverter valve from operating correctly in HTG mode....isolate the cold feed under the boiler and see if the heating improves...if it does fix the leak.

Otherwise after 7 or 8 years the wax element in the front section of the diverter becomes sluggish. Remove the right hand side panel. Put the heating on. The boiler will fire up and the pump will circulate the water within the boiler. On the right you will see the flow and return pipes to the heat exchanger (flow at front). With the temp control at max these pipes will get up to 80 centigrade or so. The burner will then shut off and water will continue to circulate. After a minute or so the heat from the circulating water is conducted through the diverter body to the front section warming up the wax element. At the "trigger" temperature the wax expands operating the rear diverter section. The return pipe should them become cold with water from the rads.

If the 2 small grub screws in the diverter can be shifted it is possible to change the front section only otherwise change the complete valve.