Please; help and guidance required. Thanks. Having recently experienced hot, cold, hot cold stream of water whilst having a shower I contacted a local plumber. Who advised me the heater exchanger unit within my Worcester 28CDi was kaput and required a new one. OK agreed with him to install a new one. But, the problem still exists!!! I'm in the proceeds with contacting the plumber to check-out the problem again. But, in the mean time is there anybody who could provide advice/guidance of what could be the provide of not getting a constant stream of warm/hot shower water? Thanks.
Is it the older Cdi or the Greenstar version? Not that it matters too much. Before checking the plate heat exchanger he would have been wise to have a look at the thermistors, these are temperature sensors which when they fail give you those very same symptoms. when you change the DHW one its worth replacing the CH at the same at the same time
Thanks Dave for your sound advice. My 28CDi is the older version. If my memory serves me right? It was installed approx 10yrs ago. So, these thermistors/sensors, could a handyman replace/install? Or is the advice use a trained plumber? Any and all advice would be much appreciated. Thanks.
If your confident in isolating and draining the boiler then its not a hard job, but be aware those isolation valves under the boiler can often weep when disturbed which can be a real pain for such a simple job. The draining procedure and part replacement guide should all be in the boiler installation and servicing instructions. If you don't have a copy its available on the Worcester website under literature. That will also give you the part number for the thermistors which you can either get online of pop into somewhere like parts centre or an independent supplier.
Neither thermistor are inside the combustion chamber and no gas parts need be disturbed to change them
A boiler that old doesn't warrant any wasted time & £££, it's highly inefficient ( guessing 50% ), probably scaled/sludged to near death, the rest of its controls are due to conk out any day soon, it's big, noisy, unpredictable & winter is upon us. We can fit boilers with a 10yr warranty, 91% eff/Band A, scale reducer, system cleanse & inhibitor, wireless programmable room stat... And all this included for only £2000!!!
Redwing, turn any hot tap FULL on and wait for the hot water to arrive. Does it stay hot? Now turn the tap to half flow -does it now go cold (boiler switches off)? If it does, post back and I'll tell you what's up with it. Tappy,
Yes Tappy. How you described is exactly what happened. Hot tap full on, cold water flow, DHW demand indicator comes on, after a few seconds Flame indicator comes on, wait until water gets fully hot, turn hot tap back to half flow, both indicators turn off, cold water flow. Thanks, Mike.
Whoops, I was going to tell you that it's probably a faulty flow switch!! Shows you just what complexities these ruddy combi' boilers are! I would go with Ddgy Mike. Tappy,
G&W Plumbing, your first post above says: "If it's on all supply's then If it's got a flat plate then it is blocked" from which I presume you mean the heat exchanger plate? Y'know - the only part the guy has actually replaced? You then claim "it's highly inefficient ( guessing 50% )" - and you are talking about a condensing boiler from a reputable manufacturer? And you throw in; "probably scaled/sludged to near death..." and a further assumption that the 'controls are about to conk out'. Phew. Can I ask - were you sucking audibly through your teeth as you typed all that?
Dave, Crows and Itchy - how would you have approached this repair? Would you have gorn straight for an expensive replacement exchanger or are there other tests you could have carried out before hand to eliminate the need to have changed the 'changer? Once Redwing has had the problem fixed, he should at least expect the exchanger to cost him no more than wholesale price...
Having attempted a couple of ways and means so that I can enjoy a warm/hot shower, I find that switching on the CH option 2-3 minutes prior to a shower and keeping it on whilst having a shower, the water temperature is acceptably warm/hot throughout. Is this piece of information helpful for anyone's thoughts of the reason for my problem? Thanks.
Had I been on site it is always easier to diagnose as you go through a mental check off list for each fault and if in any doubt use manufacture instructions or their technical helpline. I have to say I rarely have to change a plate heat exchanger. If there full of sludge a descale usually works and is half the price. The thermistors can be tested for resistance and being on site looking at the boiler would remind you that the is a Giavano style diverter valve with a diaphragm that is the most common cause of failure. Ill be honest I forgot about it in this case partially for not being in front of the boiler and partly from not working on that particular model for ages, they are becoming rare as they are slowing being replaced with more efficient models. I feel that redwing should contact his first installer and ask for the diaphragm to be fitted FOC. Ironically to get to the diverter valve on these boilers the plate heat exchanger has to come out where it can be given a visual examination for scale.
To suspect that the plate heat exchanger was partially blocked I personalty would have expected an additional complaint of some boiler noise. I don't think the first installer will come back, although we all make mistakes, even doctors do! Tappy,
A fair answer, Crows. However, if it does turn out that the exchanger wasn't at fault, then I would expect some comeback - why should the customer pay for a mis-diagnosis?
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