Pump or system fault?

[Sid Viscous]

Hi all, waddya reckon? Been to a 'breakdown' today, Potterton Puma 80. The chap's got loads of hot water but no c/h.
1st checked sytem pressure, all good & guage not jammed (it fluctuated as pump came on & off)
2nd checked pump was actually running. Yes but noisy. Using screwdriver stethoscope trick I could hear air whirring around, presumably coz water not actuall going anywhere.
Next proved diverter valve microswitch, all good with that.
The c/h system is in microbore (ALARM BELLS!)
Next the cutomer tells me the house had been empty for a couple of years before he moved in a few months ago, and that the heating had been working fine until last week. No rattling, no clanging & banging.
C/h flow pipe getting hot for 1st couple of meters, return not warming up at all. The boiler is also short cycling.

My instinct is to drain down, sweat off the manifolds & clean em out, refill with a bottle of F1 & see how that goes. If anyone's got any ideas of a boiler fault that might be to blame, I'd like to hear them. Never heard of a combi doing dhw but not heating, usually the other way round innit?

 

[tamz]

I'd start by taking the pump head off. The impeller may have jambed when the house was lying empty and sheared off.
That will take you 5 minutes to check before you start cutting pipes.

 

[stevetheplumber]

is this the one with the wax capsule that failS

 

[tamz]

Good shout Steve. I forgot they had that daft capsule on them.

 

[Sid Viscous]

Sorry, wax what? What ya on about?

 

[tamz]

There is a wax capsule head on the diverter valve on the flow pipe inside the boiler. Get a hold of the manual it will show you.

 

[Sid Viscous]

OK, cheers for the heads up. I'll have a look

 

[Sid Viscous]

Got it! Wax capsule head on diverter valve assy. Is that the one?

 

[vern]

Got it! Wax capsule head on diverter valve assy. Is that the one?

Yep common fault as is Myson CP61 pump, replace with CP63 or new boiler Puma was the pits!

 

[sky]

i agree pump

 

[diamondgas]

Most common fault that causes this is a dripping/passing hot tap ...

 

[Sid Viscous]

As I said on OP, the house was unoccupled for a couple of yrs until recently. Anyway, what's this bit of wax for, what's it do, how's it do it & why? Got the MIs but they don't really explain much. Seems like a rubbish idea to me

 

[diamondgas]

As I said on OP, the house was unoccupled for a couple of yrs until recently. Anyway, what's this bit of wax for, what's it do, how's it do it & why? Got the MIs but they don't really explain much. Seems like a rubbish idea to me

wax capsule acts to divert water flow at the diverter. It sits in the cold mains inlet. Turn on a hot tap and the capsule is cooled by the water and contracts closing off flow to the radiators. Turn the hot tap off and the pump continues to circulate hot water through the diverter. This heats up the water and brass around the wax capsule, it expands and opens the diverter allowing flow to the radiators A dripping hot tap keeps the capsule cool stopping the expansion and thus heating operating correctly!! easy way to check if this is the case; turn off the mains supply to the boiler

That's my understanding anyhoo's

 

[Sid Viscous]

Nice one Diamond, still seems like a poo idea! As I mentioned in the OP, the flow pipe is getting quite hot over the 1st 1.5m where it disappears into the floor void but it's not getting around the system. That's what makes me think of gunged up manifolds

 

[diamondgas]

Nice one Diamond, still seems like a poo idea! As I mentioned in the OP, the flow pipe is getting quite hot over the 1st 1.5m where it disappears into the floor void but it's not getting around the system. That's what makes me think of gunged up manifolds

hot flow/cold return does indicate poor circulation. 1st port of call would be as mentioned previously. Isolate cold main supply to boiler and see of the flow rate to the heating increases. Otherwise consider that the capsule is faulty and not opening the diverter enough to allow flow to the radiators. Not uncommon but more down the list of possibilities would be sludge IMHO!..... All depends on system age, design and other muck contributing factors such as open or sealed system?