Potterton Puma 80e combi poor hot water

[Allgoode]

Hi guys,
Got a customer with this old boiler. I've serviced it for last couple of years but no major issues so to speak.
Recently it has started having poor hot water performance, initially hot but then goes to tepid if that with occasional very brief blips of warmer temp water.
It switches over from central heating ok, diaphram flow switch operates correctly burner goes out for short time then re-ignites with good full flame. Hot water gives good initial splurge & then drops off.
Flame bounces about between full flame to pilot & anywhere in between.
Looking for a bit of guidance/inspiration,
Cheers,
Andy

 

[sammathias]

Partially blocked plate hex? Boiler firing on and off water hot cold hot cold..

 

[jtsplumbing]

No plate HEx on these boilers, uses main HEx try replacing the DHW limit stat first, cheep part.

 

[Allgoode]

Hi again,
Water pipe temp does not really vary in temp post initial hot splurge but the flame bounces around.
Tried Baxi tech but not much cop & suggested most of the water components & thermisters which are avail but costs would add up just to guess.
I thought of the dhw temp sensors flitting/going in & out of range which could give you the bouncing of the gas flame.

 

[Frog67]

Blocked inlet strainer?
Check resistance readings on hot water sensor?

 

[jtsplumbing]

Hi again,
Water pipe temp does not really vary in temp post initial hot splurge but the flame bounces around.
Tried Baxi tech but not much cop & suggested most of the water components & thermisters which are avail but costs would add up just to guess.
I thought of the dhw temp sensors flitting/going in & out of range which could give you the bouncing of the gas flame.

temp sensor should reed between 7 & 15 ohms if not faulty sensor, if ok may be main board.

 

[masons]

temp sensor should reed between 7 & 15 ohms if not faulty sensor, if ok

really ?

 

[jtsplumbing]

really ?

That's what it says in fault chart !!

 

[masons]

That's what it says in fault chart !!

well theres certainly a big difference between 7 and 15 ohms and 7 and 15 Kohms ( as in thousands ohms )

 

[jtsplumbing]

well theres certainly a big difference between 7 and 15 ohms and 7 and 15 Kohms ( as in thousands ohms )

Sorry fault chart if found was not very clear it is reading in Kohms

 

[Gary80gas]

What did fault turn out to be? always nice to have a conclusion.

 

[Allgoode]

I was sure i posted the solution, must be getting late.
It was the DHW temp sensor that was the culprit.
Connected the new temp sensor up dry & put demand for water in, boiler worked correctly, full flame & dropped flame when i put sensor in warm water so isolated water supply, drained water & fitted it.
Water back on, boiler held on pilot light whilst i purged air out of system & then switched control to allow full flame.
All ok now, just the other baxi post boiler to sort next with potential new bits not much shy of £200 before labour.