Halstead Quattro Gold Lockout

[lomper]

Hi
I have a Halstead Quattro Gold Combi boiler which has been fitted for about 10 years.
For the last year or so I have been having an problem with ignition lock out, I've had a plumber out and he said there was no fault. I have just flushed it out and there was only slightly grey water but still the fault persists.
The boiler fires up ok on both central heating and water and turns off when the temperature is reached, the problem is at times it will not fire back up to keep the heating hot and to heat the water, I press the ignition lock out button and it works. Recently things have got worse, at times it makes some horrendous noises in the boiler and the overheat lockout light comes on, I reset it underneath and it fires back up. It then makes the noises again and locks out, does this 3 times then works.
Could anyone help me identify what the problem could be?

Thanks

 

[gas4you]

Could be the pump intermittently sticking. If it is overheating it must be to do with lack of flow through the boiler.

if the noises are banging noises then this points to that as well.

Could possibly be the DV sticking as well.

 

[lomper]

Thanks for that Dave, had a diverter valve replaced a couple of years ago, and yes the noises are banging, I'll have to get someone out, the trouble is, it doesn't have the fault when someone looks at it!
Is a new pump a costly job?