Potterton Puma 80e - DHW going hot/cold/hot/cold

Discussion in 'Plumbing and Central Heating' started by Crazi, 16 Jul 2005.

  1. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    The hot water fires up, and the water gets hot. Then the flame switches off and only switches back on again when the water has gone cold. Swapped DHW & OverHeat thermostats, didn't help.

    Please help
     
  2. Sponsored Links
  3. gazthepottertonengineer

    gazthepottertonengineer

    Joined:
    21 May 2005
    Messages:
    1,294
    Thanks Received:
    134
    Country:
    United Kingdom
    i would say most likely to be the temp thermistor but could also be down to the fact that the h/exch is scaled up whats the flow like through boiler ?
     
  4. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks for gettting back to me Gaz.

    The water flow is not the greatest . How would you clean out the H/exch?
     
  5. chrishutt

    chrishutt

    Joined:
    20 May 2005
    Messages:
    5,343
    Thanks Received:
    21
    Country:
    United Kingdom
    Crazi, I think you need to be more precise about hot water flow rate. Open hot tap fully, time how long it takes to fill a container of known capacity (e.g. 1 litre bottle, 5 litre bucket, etc.). Then post these figures, from which we can calculate flow in litres/minute.
     
  6. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    Just been having a look - when the heating is on and we request DHW - the water remains hot. The machine fires up and everything works fine. However as soon as we switch the CH off the water goes back to hot/cold/hot/cold.
    ie.. when requesting water in "Winter" mode the temperature seems to stay constant but in "Summer" mode it goes hot, cold, hot cold.....
     
  7. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    Chris, it takes 25 seconds to fill up a 1litre bottle.
     
  8. chrishutt

    chrishutt

    Joined:
    20 May 2005
    Messages:
    5,343
    Thanks Received:
    21
    Country:
    United Kingdom
    Which is a flow rate of not much better than 2 litres/minute - should be around 9 litres/minute. Looks like a severe blockage.
     
  9. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    Chris - So my flow rate is at best crap :( .... Could this be making the thermostat act wonky? ie.. it's not switching back on fast enough because the flow rate is way too low so it's sensing the temperature difference too late?

    I forgot to mention that I replaced the Limiter last year because pressure seemed to be dropping and this didn't help. Could the flow switch be faulty and making the limiter stop the flow? or am I being a silly female :) ...lol

    Gaz - you are a local Potterton engineer. How much to get someone to service/clean the heat exchanger and how do they clean it properly so I can watch and make sure they are doing it? I am worried about paying for a service and the guy just takes the usual meter measurements, leaves and says "that's all normal"....

    PS... Someone has mentioned the wax capsule head and wax capsule to me - What do they do? Looking at the diagram they look like they are just switching the diverter CH so i don't think they have much to do at all with my DHW pressure?

    Appreciate you guys patience :)
     
  10. Sponsored Links
  11. chrishutt

    chrishutt

    Joined:
    20 May 2005
    Messages:
    5,343
    Thanks Received:
    21
    Country:
    United Kingdom
    I'm not an expert on Potterton boilers (unlike Gazthepottertonengineer) but I'd say the very low flow rate was the problem. Probably just at the threshold for operating the flow switch. When water heats up, flow decreases (not sure why, but it always seams to!), then flow switch goes to off, then water runs cold, flow increases again, flow switch operates, etc.etc.

    The question is "what is restricting the flow?". Could well be scaled up secondary (DHW) heat exchanger as Gaz suggested, but other possibilities should be considered. For example is cold water flow adequate (i.e. more than say 10 litres/min), are isolating valves on boiler fully open, is hot water flow equally poor at all outlets (taps)?
     
  12. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    Cold water pressure is good. We had them check it and I believe it was about 4bar. We get about a litre every 4/5 seconds or so. All inlet valves are fully open and the hot is bad at all hot water taps.

    I think from your explanations I have a blockage :( ... Time for a British Gas engineer I think. Are BG engineers any good?
     
  13. Agile

    Agile

    Joined:
    26 Jun 2004
    Messages:
    64,039
    Thanks Received:
    4,595
    Location:
    London
    Country:
    United Kingdom
    I did ask you what was the "limiter" which you replaced and where was it located but it seems my post has been deleted!

    My thought is that you are better getting an independent engineer who is familiar with the boiler as the costs are likely to be lower. BG engineers sre not always very good with Pumas and are likely to recommend a new boiler. Potty engineers are likely to be very competent with that model but are likely to be significantly more expensive as I dont think it is a very serious problem.

    Tony Glazier

    MOD

    why should your post have been deleted ??
    as you have been asked before Mr glazier pack the snide digs
     
  14. Agile

    Agile

    Joined:
    26 Jun 2004
    Messages:
    64,039
    Thanks Received:
    4,595
    Location:
    London
    Country:
    United Kingdom
    To anonymous Mod,

    Kev? he often calls me "Mr Glazier" in such a manner rather than a more friendly "Tony".

    Perhaps YOU can tell me why it may have been deleted?

    Thats why I dont feel comfortable posting here, unexplained deletions and unfriendly comments by anonymous moderators.

    Tony

    MOD

    it wasnt deleted
    you pressed the wrong button
    as in it was never posted ;)

    as you have been informed on more than one occasion if you dont feel comfortable posting on here
    DONT
     
  15. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    The limiter is located at the output of the hot water. Also connected to the flow switch. This is what potterton told me to replace when the pressure was falling but it didn't help at all :(

    BGas has offered to come and fix it as part of a maintenance contract. As it needs repaired they say it is £24 pm for the first year then it falls back to £16 pm.

    Does these prices sound ok as the boiler is now 5 years old?.... I said yes to get the thing serviced and if there is a blockage hopefully get it fixed.

    He's coming on Thursday. I will keep you guys updated and once again thank you all for your help! Us ladies need guys like you around :)
     
  16. gazthepottertonengineer

    gazthepottertonengineer

    Joined:
    21 May 2005
    Messages:
    1,294
    Thanks Received:
    134
    Country:
    United Kingdom
    Crazi i would have to say especially if you havent got a scale reducer fitted that it sounds like the heat exchanger is scaled up :cry:
    this particular type of h/exch is very prone to this as it is a crossflow heat exchanger which is all part of the main h/exch :confused:

    potterton would charge £275-00 inclusive to replace this ;)
     
  17. Crazi

    Crazi

    Joined:
    16 Jul 2005
    Messages:
    20
    Thanks Received:
    0
    Country:
    United Kingdom
    Gaz - do they replace it - or clean it?
     
Loading...

Share This Page