Little help please?

[Gr fto reborn]

Got a call customer has no hot water. So turn up they tell me the potterton prima f60 had been making a noise and over heating. They had been resetting the over heat. But it only happens on hot water. So I pop upstairs to find a sticking Drayton 3 port. I swap that to a Honeywell and all is good. No sticking, boiler firing on command. But then it over heats again. Pumps circulating but only upstairs rads have got hot. Maybe the pumps just seen better days so I replace that. Still the same as what it was. Client tells me the boiler only over heats on hot water demand. Or first thing in the morning for heating. Plus downstairs rads are still cold. Any ideas. I thinking a good flushing may be in order. Just want to know if I'm right? Help is greatly appreciated.

 

[bspareltd]

did a job like that this week, pump seems as if it is spinning but shaft has snapped .
Always remember heat rises , that is why the downstairs rads are cold .
Lets put it this way if it isnt the pump I will take my pants off and run down the road with my tool box.

 

[bonesy60]

I think he says that he has replaced the pump from my understanding so cant be that.

 

[on31ll]

Well take off your pants and get running ! The OP has said he has also changed the pump hasnt he ?

 

[on31ll]

I think he says that he has replaced the pump from my understanding so cant be that.

Sorry you beat me to it !

 

[Gr fto reborn]

Yep changed the pump hence my confusion. Just frustrated me that it over heats only in the morning and on hot water. It's like heat isn't getting out of the heat exchanger fast enough after the boiler thermostat has clicked in and pop goes the overheat stat.

 

[garyplumb]

Possibly a blockage somewhere?

 

[darren bastin]

I assume this is open vented ? . If so cut out the h or air seperator and see if its partially blocked. Had quite a few mysteries solved by this.