Worcester Combi Boiler - No Hot Water

Discussion in 'Plumbers' Talk' started by Pagloss, Jan 12, 2015.

  1. Pagloss

    Pagloss Member

    I would appreciate it if anyone out there could give me some advice on a boiler problem i've got. I have a Worcester Greenstar 28i Junior Combi boiler. The heating is working perfectly but I am have no hot water. When I turn a hot tap on the boiler fires up and hot water is initially produced but within 10 to 20 seconds the water goes cold again. The flow from the tap then starts to slow to just a trickle and I have to open it up further to get a flow but then the water only runs cold and no matter how long it runs it never heats up again.
  2. When you open your tap up further, is actual flow fully restored? (Some 'washer' taps do partially shut themselves off when they get hot water coming through due to expansion of the internals. Do all your hot taps have a 'slowing flow' to a trickle?)

    Ie - I'm trying to work out if there's a 'blockage' in the boliler, or just that the hot water stops being heated.
  3. Pagloss

    Pagloss Member

    Yes when I open the tap up further the flow is fully restored but the water is cold. The same thing happens whichever hot tap I try in the house.
  4. Dave does Gas

    Dave does Gas Screwfix Select

    Problem with your plate heat exchanger, It either needs a de scale or replacing. It's a pig of a job on those juniors, the entire hydraulic block has to come out to access it.
    Any one who says Worcesters are great boilers has clearly never had to work on one.
    macdog1983 likes this.
  5. Pagloss

    Pagloss Member

    Thanks Dave. I have just tried it again and ran the tap whilst I stood next to the boiler. What happens is the boiler fires up and seems to be heating the water and then it shuts off again after a minute or so, hence the cold water I guess. Also once it shuts down there is a clunking/grinding noise coming from within the boiler, it only lasts a second or so. Does this confirm your diagnosis or does this mean it could be something else. Before I came on the screwfix forum I did a quick search online to see if anyone had similar boiler problems and faulty diverter valves was mentioned whatever that is.
  6. brian burgess

    brian burgess New Member

    My guess & im usually wrong , & im not a plumber either diverter valve!
  7. Thanks, Pag.

    If the taps open up again with an extra tweak, I guess it's chust a characteristic of the taps - so nothing to do with the boiler.

    The boiler issue sounds like wot Dave says - and it's exactly what I had too with my GlowWorm.

    It was caused by a slow build-up of sludge inside the PtoP exchanger, the one wot heats the DHW. What happens is that the internal waterways in these exchangers are so narrow, that a coating builds up to the point the boiler can no longer force through the 'boiled' water into it. Classic symptom - it starts off fine and then runs cold after, ooh, 20 seconds, a minute, whatever.

    If you leave it running, it may well (at early stages at least) fire up again for another bash. Only to shut down again.

    Do you have a filter fitted in your system - a Magnaclean or similar? If so, does it catch regular coatings of sludge?

    Ok, a replacement exchanger is - ooh - £200? And it sounds like a couple of hours work from wot Dave says. So you'll have little change oot of £400. Happy New Year.

    Ok, if you don't have a filter fitted, and if you think there's a fair chance it could be down to 'sludge', this is how I fixed mine...

    I bought a Magnaclean and installed it just below the boiler on the return. I also bought a couple of bottles of Sentinel X800, the 'powerful' one...

    I filled the filter housing with X880 - it took a half bottle each time. I then fired up the CH and after a couple of seconds turned on a hot tap full. Ran that for a few seconds, and then offski. And back on after a further second.

    On for 20 seconds, then off for a couple, then on then off then on then off then... you get the idea.

    Ok, my hope was that the concentrated X800 would have gotten as far as the boiler when I turned on the DHW. This concentrated dose was then sent flying around in circles between the main exchanger (where the burner is) and the PtoP ('secondary') exchanger which is the one that transfers this heated water to the hot tap flow.

    As long as the hot tap is on, the same small amount of water goes around and around the boiler between these two exchangers. I hoped that this concentrated X800 would start to clear the sludge in the secondary exch.

    This is what actually happened - it worked.

    The second time I turned on the hot tap, it ran hot for 30-40 seconds instead of the usual 5. The next time it stayed on for a couple of minutes. After that it simply worked...

    I had a filter fitted which cost around £80 - and which I really needed anyway - and a couple of doses of X800 which I got cheap on t'Bay for about £12 I think it was.

    I left the X800 in the system for longer than I 'should' have - around 2-3 months - and cleaned out my filter every fortnight or so - a goodly 1/8th inch coating came out each time.

    After this time, I connected a hose to my system (where the filter is fitted) and flushed through for a good while - the water was brownish if seen in a bucket, but nothing horrendous. But it just doesn't take much to slowly block an exchanger.

    Now I have X400 in there to keep the cleaning going. I'm not too bothered about how long that stays in tbh...

    So, if you do have a blocked PtoP exchanger and you don't have a filter, I know what I would do.
  8. Pagloss

    Pagloss Member

    Thanks for all the advice folks. I'll let you know how I get on.
  9. Dave does Gas

    Dave does Gas Screwfix Select

    DA's method may work but is very time consuming with no guarantee of success if your secondary heat exchanger is beyond repair.
    If I was on site I would offer you two options,
    1) Remove the heat exchanger and descale it using a de scaler like Fernox DS4
    2) Replace the heat exchanger with a new one.
    You have to bear in mind that to access these heat exchangers the entire hydraulic block has to come out. Dependant upon where your boiler is sited it can be a pain or a real pig to do this as Worcesters are not the best boilers to work on.
    Given the work involved and option 1 does not always work,option two would probably be favourite as with the heat exchanger all the washers and O rings are included.
    You should also consider as DA states fitting a Magnaclean or similar flitter to prevent this re occurring.
    You will probably be looking at about £300.00 ish

Share This Page