Potterton Kingfisher 80,000 Btu (2001)

[Bennidi]

After years of perfect operation the boiler has starter (intermittently) to overheat the water (when on domestic only) making it boil up and overflow into header tank. Cured by turing off (at timer) and straight back on. Thermostat replaced, system flushed out, Plumber baffled.
Any ideas?

 

[Agile]

I would want to ask what kind of thermostat has been replaced.

Its much more likely to be a water flow problem. What has he done to check the water flow and pump operation?

If the pump is OK then it will probably be sludged up but lets hope not as thats more costly to deal with.

If you can advise us of the flow and return temperatures at the boiler that will give a very useful indication of the problem.

Tony

 

[Axel]

Pump on that is usually connected to boiler PCB, which controls the overrun, so if resetting boiler (PCB) cures problem then it could be related to PCB, unless pump is jamming and restarting when turned back on.

 

[Bennidi]

I would want to ask what kind of thermostat has been replaced.

Its much more likely to be a water flow problem. What has he done to check the water flow and pump operation?

If the pump is OK then it will probably be sludged up but lets hope not as thats more costly to deal with.

If you can advise us of the flow and return temperatures at the boiler that will give a very useful indication of the problem.

Tony

Thanks for that - very prompt. The first thing (I forgot to say) is that on domestic it is gravity only - the pump only coming in for the rads. (I know they say all pumped is more efficient, but it worked Ok like that for 8 years.) Parts replaced were potentiometer, thermostat and overheat limit switch. It could be that the coil is a little sludged up but when the problem occurs, in most cases, the return pipe is almost as hot as the out pipe, so it must be circulating reasonably well. And there is no problem with its ability to make a good tank of hot water. What I am now trying - since this morning - is to keep the temp switch down very low, rather than about halfway.

 

[Axel]

When you say 'Thermostat' do you mean the stat on the boiler, or the cylinder stat? You should check the correct operation of the cylinder stat.

 

[Bennidi]

When you say 'Thermostat' do you mean the stat on the boiler, or the cylinder stat? You should check the correct operation of the cylinder stat.

Sorry again for inprecision: the thermostat on the boiler. There is no independent thermostat on the tank.

 

[Axel]

There should be a cylinder stat somewhere on the side of your hot water cylinder, to tell the boiler to switch off when the DHW in the cylinder is hot enough.

Untitled

• Axel
• 27 May 2010
• 1

 

[Bennidi]

There should be a cylinder stat somewhere on the side of your hot water cylinder, to tell the boiler to switch off when the DHW in the cylinder is hot enough.

Untitled

• Axel
• 27 May 2010
• 1

Halloa again.
There isn't unfortuantely.
But it isn't the cyclinder that has the water too hot. It is the pipe that goes through the boiler. That seems to get too hot too quickly while the cyclinder is still heating up. And that makes it go up the overflow instead

 

[Axel]

Pump, electrical supply to pump (possibly from boiler PCB), or blockage then.

 

[Rob]

Sounds like a board fault, have experienced it before. Do you also notice it cycling on and off quite rapidly?

Bit silly these boilers though...

You can disconnect the thermistor and it will still work and the OH stat isnt fitted directly to the flow pipe which means its basically redundant hence the water boiling.

 

[Boilerman2]

Where the hell is the PCB on a Potterton Kingfisher FFS?????
It sounds like the OP has a Gravity Hot Water System, with pumped heating, which would explain the absence of a Cylinder Stat, But as for PCB Controlled over run NO WAY!! (only the much newer Kingfisher MF has a PCB with whistles & Bells!!)

 

[Andygasman2010]

Where the hell is the PCB on a Potterton Kingfisher FFS?????
It sounds like the OP has a Gravity Hot Water System, with pumped heating, which would explain the absence of a Cylinder Stat, But as for PCB Controlled over run NO WAY!! (only the much newer Kingfisher MF has a PCB with whistles & Bells!!)

The op said he'd changed the potentiometer and that it is a 2001 model. Sounds to me like it is the later model with a PCB hooked up to a gravity system

op - what's the exact model of your boiler?

 

[Boilerman2]

The OP does say Potentiometer replaced so it may be an MF version, I don't have a manual to hand for this boiler, but I suspect it should only be used on a fully pumped system???

 

[Andygasman2010]

I suspect it should only be used on a fully pumped system???

I was thinking the same thing too! Just found a manual for the MF version and it does say it can be installed on a gravity system so given that the potentiometer has been changed it may actually be the PCB. It'd be a rare fault mind..!

 

[Rob]

The MF does support gravity but it requires a modification to the OH stat which as I said seems to make it redundant.