Newbie to Gas and Plumbing need help with Performa 24 lockout issue.

[Gaslite]

Hi everyone,

Although long in the tooth I'm quite new to the world of gas/plumbing and boiler repairs. I have found a lot of useful info on this site already but I could do with some help with a current problem.

A customers Potterton Performa 24 keeps tripping the Safety Limit Thermostat. The CH appears to be working well and the DHW flow is good and a decent temperature rise. I have noticed that when the hot tap is turned off the DHW diverter pin takes a relatively long time to retract, typically 10-12 seconds. (I've noticed on similar models the pin moves more or less instantaneously, certainly within a second or so). I'm assuming that because of this delay with the burner on full with no water flowing and this is tripping the Safety Limit Thermostat. I have replaced the DHW pressure diff. diaphragm and cleaned a greased the pin and they appear to move freely. What could be causing the slow retraction of the pin? Any help greatly appreciated.


Have a great Easter break,
Gaslite

 

[Billy Bob Bob]

did you change the stuffing box?,it normally comes in the new kit,could have a sticking diverter this will cause it to over heat

 

[Gaslite]

Thanks for your prompt reply Gasman.

I did not change the stuffing box, I just backed it off slightly. I just bought the diaphram as I was not aware of the service kit at the time. Is the diverter serviceable and is there a service kit available? The manual just gives the short parts list, not sure where to access the "long" parts list.

Regards,
Gaslite

 

[Billy Bob Bob]

buy the kit and try a stuffing box,the diverter sadly is not serviceable so it would mean a new one

 

[diamondgas]

IF it's not a sticking pin, which you say you greased, there may be a 'dead leg' full of air on the hot water pipe circuit. This can cause a fault similar to what you describe...

 

[Gaslite]

Thanks Diamondgas,

How could I purge the air if this is my problem.

Regards,
Gaslite

 

[diamondgas]

Well Gaslite you need to find it first. I usually start with questions; any work been done that's drained the hot water, any changes in system design, bathrooms...etc then the usual places to look are where the old cylinder, hot water storage tank was. Sometimes a combi is connected to the nearest hot pipe and the cylinder pipes are caped where they were cut off. If it is a dead leg this cap may be compression in which case you just need to crack it to let the air out! A bit of investigation will determine whether it's a dead leg or not. Another indicator of 'dead-legs' is when a cold tap is turned on or off the boiler lights briefly even though there's been no demand ....

 

[Billy Bob Bob]

while i agree a dead leg would make the pin slow to retract it will not cause the performa to go into overheat if this is a standard efficiency performa and not HE it would have been installed a few years so i would have thought if it was a dead leg the problem would have been a issue before now IMHO

 

[Gaslite]

Thanks Diamondgas,

Could well be air as you say as this problem started after the system was drained down.

Regards,
Gaslite

 

[Billy Bob Bob]

was the hot drained down to do the repair?

 

[Gaslite]

Yes, it has been partially drained down several times. The initial callout was due to zero system pressure, the filling loop had a slight leak and was replaced. called out again within the week as system pressure dropped to zero. The customer was running a bath when the mains failed due to local building work. Not sure why the system pressure dropped to zero. Once the water board had re-established the water supply the boiler was re-filled, the temperature thermostat had failed the safety thermostat had tripped and coincidentally the DHW micro switch failed, causing the boiler to cycle. Since then the safety limit thermostat has bee tripping with increasing regularity.

 

[Billy Bob Bob]

it could be a dead leg in that case but this wont cause the overheat on its own,is the aav working?

 

[Gaslite]

Thanks Gasman, I will check the AAV when I go back to site on Tuesday, thanks for you advice.

Regards,
Gaslite

 

[Billy Bob Bob]

no probs let us know how you get on

 

[diamondgas]

look forward to what you find gaslite...

 

[PlumbBobBob]

hi welcome along