Over heating combi

[bunser]

My radiant combi boiler is flashing the over heating warning light when I use the hot water. Any ideas please.
Thanks

 

[kevplumb]

try a search i seem to remember a similar problem a while back

 

[Paul Barker]

Not familiar with that boiler but is the pressure low?

 

[bunser]

Water pressure is fine. the pump sounds like its running, although perhaps it may be running slow but I don't know how to check pump speed. I have had the heat exchanger out and it's totally clear. Cleaned the pump head. Changed the diverter valve cartridge because it was sticking. There is a sound of bubbling though.
Thanks

 

[kevplumb]

check the air vent

 

[bunser]

Checked and vented.
Thanks

 

[ChrisR]

Main heat exchanger blocked?
Faulty stat?
Take the pump head off - is the impeller blocked? Try running it for a few seconds - can you stop the pump with one finger? It should be really difficult. Check the rpm printed on the endprobably. SLow is often Very slow.

 

[bunser]

Main heat exchanger Clear, had it out and flushed it.
Had the pump head off, no blockage. How do I run the pump head when it's off?
Any ideas how to test pump rpm, multimeter?
Thanks

 

[chrishutt]

To check pump operation/speed, remove screw cap to expose end of pump spindle. A small amount of water should seep out while the cap is off - this is normal. You should be able to see the spindle end rotating, and indeed feel it with your finger.

 

[bunser]

So if I can stop the end of the spindle with my finger, the pump has had it?
Thanks

 

[DP]

Instead of guessing, why not put a digital thermometer on the input and output of the heat exchanger (for a start) and take temperature readings. As the heat output builds up, the thermostat sensor (on the output usually) should interupt the power to the gas valve. Move the temp probes about to take other readings to get a better ideal to locate excessive temperature drop (hence) blockage

Pump spindle should rotate freely. Any sticky spots are cause for concern. While it might be OK to run the pump dry (on the bench), prolonged running might damage the pump, since system water lubricates the bearings.

 

[bunser]

Thanks for everyones input. If I find the problem I will let you know.

 

[Scalgon]

Bunser. Do you live in a hard water area?

 

[bunser]

Yes, the PH level is 17 - 18.
Thanks

 

[Agile]

I presume that with a PH level of 17-18 that all your plumbing must be in plastic piping !!!.

Are you 100% sure the flashing red is meant to indicate overheating?

Tony Glazier