Combi 80 runs for a few seconds then stops, then lights agai

[chowza]

Hi can someone please help me.

My Potterton combi 80 when there is a heating demand, will light the main flame, the pump and fan are both running then after about 10-15 seconds the flame and fan will stop, this whole thing happens again about a minute later, and keeps happening.

I thought that the pump was to blame and not moving the water around the system quick enough but it is still the same after replacing that.

The radiator do get hot but they take a long time to warm up.

If i run hot water the boiler works fine even for a shower. The problem is just with the central heating side.

PLease suggest some possible solutions.

 

[Whiter]

Don't now much about these boilers but have you tryed testing the heating thermister, may be able to swap with H.W. thermistor if your lucky.

 

[ChrisR]

They are the same but wet.

More likely diverter /waxstat is only part working - stuck on HW side.
On CH does the boiler make a noise like it's getting hot, if you recognise that?

 

[chowza]

The pump is getting to hot to touch and the ink on the printed label is running. the water is not actually boiling, and there is not any steam coming out of the top vent.

 

[chowza]

I have just checked the temperature around different parts of the boiler, i think that these may be a little telling of what is going on.

Directly after the burner

Top of pump 86 deg C
At temp thermistor 86 deg C
Flow isolator valve 74 deg C
Return isolator valve 31 deg C
Bottom of the pump 82 deg C

A short while after the burner ran

Top of pump 64 deg C
At temp thermistor 66 deg C
Flow isolator valve 61 deg C
Return isolator valve 37 deg C
Bottom of the pump 66 deg C


From these temperature reading it seems the water is flowing around the boiler, and not around the radiators.

I hope this gives you more of an idea, so you can help me more

many thanks

 

[Paul Barker]

Points to what Chris R said.

 

[ChrisR]

Top of pump 86 deg C
Flow isolator valve 74 deg C

So the primary water isn't getting past the DV properly

Try heating up the front end of the DV - that's where the waxstat lives. It you get it up to 80 something it might get the idea that it's hot. A new waxstat doesn its thing at 38º - I measured one once. I don't know how hot you can get them before they burst, but yours is probably dead anyway!
If matters improve you may only have to change the waxstat

How refreshing it is to get some proper diagnostic info back from the user - corgi or not!

 

[gazthepottertonengineer]

i have been to hundreds of these where it is a hot tap dripping which keeps the wax capsule in the hot water mode it doesnt take alot so check all your taps

or easier still simply turn the ballofix off under the boiler to stop the cold water going through the boiler

 

[ChrisR]

Oh yes, there is that!

 

[Agile]

Trouble with that is the CW ball valve will probably start leaking, and if you did turn off the heating circuit ball valves they will almost certainly start leaking!

Tony

 

[gazthepottertonengineer]

agreed about the heating ones
but the Cold water one is normally fine


god its hot today

 

[chowza]

Thankyou for all your replies.

It was the dripping hot water tap.

Gaz was right about the CH valves leaking.

It is extremely hot today, especially as i left the room stat at 30 degrees.

The rads are almost glowing with heat now.