Grant Combi 70 MKll Cycling

[Robert Tyrrell]

Got called to a Grant Combi 70 MKll today to find that its; cycling - 2 minutes on and 2 minutes off. The house reaches temperature but it takes a couple of hours to do so.
About 6 months back I fitted a new boiler heat control and today I've fitted a new primary store stat but it''s still cycling so ......

• Can anyone explain to me why this might be cycling?
• What the resistance values are or the boiler stat, primary store stat, and high limit stat?

I cant speak to Grant when I'm at the property as there's no landline or mobile signal so I could do with these values to test the components.
Cheers m'dears

 

[Chalked]

Is it doing underfloor?

 

[SimonG]

Not getting heat away quick enough. Sludge or pump?

 

[Robert Tyrrell]

It's not doing underfloor, it has an Adey Magnaclean filter in the system, and a new pump/diverter valve last year.
All the rads get hot, too hot to keep a hand on and the temperature in the property does rise, it's just that as the guy who owns it does it all from his office by remote computer systems, he can see how long everything takes and he's convinced that it didn't do this last year.
It took 2.5 hours to get the place up to 21 degrees (That's the max ttemp that he sets for all his properties).
I should add that when starting from cold, it will run on for about 20 minutes, the rads get hot and then it starts the 2 on 2 off routine.
I have explained to him that it will do this if the system temperature has been reached, and the room temp hasn't but as I said, he's convinced that it was different las year.

 

[Best]

Edited, as didn't read the control stat is replaced

 

[Chuck]

Can anyone explain to me why this might be cycling?

Boilers short-cycle when the return temperature is getting too high. Possible causes outside the boiler include (a) the automatic bypass valve is stuck open or has been fiddled with, (b) TRVs have stuck closed or been turned down so that the radiators are not transferring heat out of the system water fast enough.

 

[Robert Tyrrell]

Boilers short-cycle when the return temperature is getting too high. Possible causes outside the boiler include (a) the automatic bypass valve is stuck open or has been fiddled with, (b) TRVs have stuck closed or been turned down so that the radiators are not transferring heat out of the system water fast enough.

Thanks or the input - I tested the primary store stat and it had failed so I replaced it and the boiler appears to be working OK now.

 

[Best]

Thanks or the input - I tested the primary store stat and it had failed so I replaced it and the boiler appears to be working OK now.

Brand new stat failed?