hot water problem potterton puma80e

[david64eagle]

Hi All,

I have had a potterton puma 80e for about 10 years, it has always been covered by heat team.
About eight weeks ago, i turn on the bath tap and the hot water flowed for about 2 minutes then the boiler blocked out.

I checked that the water preasure dial was ok and added a small amount of water, then pressed the reset and the boiler fired again.
I waited a few minutes and tried to fill the bath again but it locked out again after about one minute.
I called in heat team and the guy said i needed a new DHW Temperature Sensor, while he was fitting it he said that I had cold water mixing somewhere in my system and that i should check the shower or other mixer taps.
Since that time I have fitted pegler shut off valves to the hot and cold supply to the first floor,
It still cut out, The only other tap is a sink mixer so I put another pegler valve on the cold side of that mixer.
I was pig sick when it cut out yet again, I had thought that this was not the cause but had to find out the hard way that this guy had it wrong.

Obviously I need to call them in and prove that its not the mixing thats causing the problem it was only a slight dribble I could pee faster..
Anyone got a possible solution?
Sorry for the long story guys!

Dave

 

[sandybeach]

Was the last call out a Monday morning or a Friday afternoon job?

I'm sure the next chap will suss it out for you seeing as you've done all that work for nothing.

 

[steve32]

Most likely cause is DHW coils in heat exchanger scaled
This is a common problem on puma's of this age.

To test you need 2 temp gauges.
Connect one to heating flow in boiler casing (front chrome on right side of combi).
Connect the other gauge to hot water out (one of the chrome pipes on left of combi)
The temperature difference should be about 20 oC when tap is flowing at approximately 9-10L min.

The temp on the heating flow should not go above 70 oC if the temp goes above 90 oC it will lock out on overheat stat.

 

[david64eagle]

Hi Steve

If it is this heat exchanger scaled, can it be corrected, because a relacement part is not available.

If not its a new boiler, what would you buy? of a similar spec

Dave

 

[ianmcd]

I would be looking at the flow limiter assembly rather than the heat exchanger