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Andrew Smith
Andrew Smith, Plumber
Category: Home Improvement
Satisfied Customers: 3629
Experience:  City and Guilds Qualified plumber
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potterton puma 80. dhw ok.[ when ch. switched on fires up

Customer Question

potterton puma 80. dhw ok.[ when ch. switched on fires up for 30 secs then burner dies
down]took diverter valve apart put wax sensor in hot water plunger extended ok.[stripped stripped dhw valve diaphram ok @micro sw ok operating ok on dhw demand][ water pump removed found ok] fitted new temp sensor.[switched on ch 24 hr boiler fires up then pressed dhw sw on manually boiler ran continually after 2mins boilerkept running ch rads heated up ok @boiler cut out ok on boiler stat][ fired up ch again same procedure as before then switched hot water tap ran for 1 min when dhw tap switched off ch come on for 30 secs shut down again ?
Submitted: 3 years ago.
Category: Home Improvement
Expert:  Andrew Smith replied 3 years ago.

Andrew Smith :

Are you able to follow the heat around, when the boiler is running for the 30 seconds - is it definitely going into the heating?

JACUSTOMER-d4h8c8al- :

hot water outlet to ch just got warm

Andrew Smith :

What about the return?

JACUSTOMER-d4h8c8al- :

return cold not enough time to go round ch system

JACUSTOMER-d4h8c8al- :

the return not enough time to go round ch system

Andrew Smith :

If there was a circulation problem, or a problem with the pump it may heat the flow return the same amount

Andrew Smith :

Rather than pumping around the system

JACUSTOMER-d4h8c8al- :

i removed pump impeller & pump ok. diverter valve stripped cleaned &re assembled wax capsule placed in hot water&opened ok.d h w valve ok.micro switch ok.all stats & frost protectors ok.gas pressure tested&right press.both solenoids on gas valve tested & ok.[d h w system working ok +reaching right temp.] [when c h switched on boiler fires up for 5 secs. then shuts off. pump stays running] [then switched on c h again & operated micro switch on d h w held on for 2 mins. then boiler kept running on c h mode heated all rads ok turned room stat. up to max & boiler cut out on boiler stat when boiler stat. cooled boiler fired up again ran ok for rest of night. [it will not fire up again from cold start. sorry for the delay but i have been really unwell charlie.

Andrew Smith :

Ok, so you have a problem firing from cold.

Andrew Smith :

When running from cold and the boiler fires do the flow and return get warm - one, both?

JACUSTOMER-d4h8c8al- :

one only felt warm at outlet behind diverter valve return pipe cold.

Andrew Smith :

ok, so we are getting circulation while it is actually running

Andrew Smith :

it sounds like the ch thermistor is shutting it down as you are not getting a fault light, but strange that it works normally once you have got it going

Andrew Smith :

Once it has fired but cuts out, is there anything that shuts down before you lose heat? The divertor valve?

JACUSTOMER-d4h8c8al- :

yes when i held micro sw on manually for two mins the ch system worked ok even firing up again after thermostat cutout and heated all rads in the normal amount of time [with ch on and running ok switched on hot water tap hot water ok turned off d h w tap for boiler to go back to c h just fired up for 5 secs then shut down

Andrew Smith :

Does the pin not extend and push the microswitch?

JACUSTOMER-d4h8c8al- :

i already said d h w valve works ok on demand for hot water [have already stripped d h w valve diapram ok pin to operate micro sw ok] hot water tap on pin pushes out ok & operates micro sw

JACUSTOMER-d4h8c8al- :

i fitted a new thermistor i tought i was getting wrong resisance reading on my ohm meter fitted new thermistor fault same

Andrew Smith :

Does your model not have one for the heating that pushes out when the pump runs?

Andrew Smith :

Let me dig out a diagram - do you have the GC no.?

JACUSTOMER-d4h8c8al- :

g c no 47 590 10

JACUSTOMER-d4h8c8al- :

it only has one sw

Andrew Smith :

Yes, you have the old one - there is a functional flow diagram on page 42 of this book;

Andrew Smith :

and mentions the LED on the modulation pcb being on or off - off for ch demand, can you check this?

JACUSTOMER-d4h8c8al- :

ok

Andrew Smith :

Let me know what you find