Worcester 28i rsf old combi

[Inverness]

issue with the boiler customer says it on for 20mins or so then turns off without the high limit button being activated? The radiators get hot and there hot water from the tap. The system is badly needing a magnet filter to be fitted which I'm doing tomorrow.
My conclusion maybe it's full of sludge and the pump isn't managing to circulate the water in time but would think the high limit button would click on. Customer any advice?

 

[spike.gb]

Is it modulating?

 

[Inverness]

It's an old non condensing combi,

 

[Gas74]

Could be Pcb or intermittent sticking pump.

 

[spike.gb]

If it's modulating is the minimum gas rate set correctly.

 

[Inverness]

Cheers guys, Hi went there today. The high limit button had been activated. The ignition process is fine but I gather the thermostat phial has a bit of a delay from expanding to contracting? The response takes a while from adjusting the temperture to max to min. Any advice? I've also fitted a magnaclean with cleaner added..

 

[Gas74]

Pcb not modulating down or intermittent sticking pump at a guess.

 

[Inverness]

It ís modulating down but it takes a while to happen, the pump might have been sludge up to why the high limit button was activated? With system cleaner and a filter added see if this makes a difference. What would the problems be if the thermostatic sensor was on its way out?