Water through hot taps not getting hot.

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I have a Worcester 28 CDI RSF boiler fitted in my loft. Whenever I ask for hot water either at the taps or in the shower, it sometimes takes up to five minutes to come through. Even then it can go cold again after a short while; perhaps a minute or so. Strangely though, if the central heating is on, it comes through hot in approx. 50 seconds! Can anyone solve this mystery for me? I have recently replaced the filling loop, but I seem to remember this problem started long before I did that. One more thing. My pressure guage on the boiler drops to around 1bar and I have to top it up and also the pipes make a ticking noise and there is air in my bedroom radiator, despite bleeding it two or three times. Any advise will be welcome!
 
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I would imagine you've got a dirty system, hot water problem could well be due to a build up of sludge in both diverter and h/ex, loosing pressure is possibly prv letting by due to muck in the valve and a lack of air in the expansion vessel, and the air in rad(s) may be gas caused by corrosion which is happening because there is no inhibitor in system.
 
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hi Mick,
thanks for your reply,the system was flushed with a cleaner and refilled using an inhibitor,the only recent work was a new internal filling loop,I have checked to see if the prv was leaking out onto the driveway beneath the outlet but it seems not to be,I will check the expansion vessel and post back,

thanks in advance

didgeradoo4719
 
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pressure drop is either duff pv or a leak
hot water problem seems to be a stuck diverter caused by dirt in the system.
chances are your flushing work did not take care of the problem
 
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Thanks to all of those guy who replied! I will have to seek local Corgi registered engineer to take a look at the boiler. Will let you know the results.

Cheers!
 
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hi all,
no apparant leak from the prv,however i have noticed that the flame does'nt seem to be full on when a demand for hot water is made,this morning i had the shower running for a good 5 mins but it was still only just starting to get very luke warm,i would say that the water is piping hot in 50 or so seconds if the heating is on then i turn hot tap on,i can hear the microswitches making when tap turned on but flame seems to stay low? any advice acepted with thanks.
 
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the gas valve might not be modulating/sticking on low gas. could be a faulty gas valve, pcb or thermistor causing it.
 
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thankyou for your reply screech,

somebody mentioed to me it could be the diverter valve or a diaphram inside it, is it possible it is this?

thanks for all help.........
 
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I've just purchased a new diverter valve diaphram kit and will fit this tomorrow (missus will want heating on tonight!) so I'll let you know if this cures the problem. I am more inclined to agree with you Screech that the gas valve might be faulty. Funny though that the central heating water is mad hot! I hope new diverter diaphram solves the problem!
 
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Replaced diverter valve diaphram ( old one looked ok! ) today, but made no difference to the hot water getting hot quick enough. Still ok if CH is on, so must be something else. Can anyone suggest any further checks I can make? Thanks!
 
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Hi Bengasman! Good question that! To be honest I only know that when I ask for DHW without the heating on the microswitch operates, the ignition sparks and the boiler lights. The problem I feel, being a novice, is that the gas doesn't increase to full flame, as I have been told it should. My brother in law is Corgi gas registered but unfortunately, he had to go away until the middle of January, so I'm trying to sort it out myself. Before he left he suggested the diaphram change, which as I have said doesn't seem to have worked. I am trying to find out what the resistance figures across the DHW thermistor should be. Do you know? I have tested the present one across the terminals and I get a reading of 14.0 on ohms, depending on the selection on the meter I get a lower figure of 0.05 if this is of any relevance? Beginning to think I may need to buy a new condensing boiler as I could be changing anything that I think may be at fault. Nobody as yet seems to be able to point me in a more positive direction; then again you might! Here's hoping and thanks for your input.
 
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typical reading for cold ntc is about 10k. can't remember the exact spec for this one, but anything under 100 when cold means it is kaput
 
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you need to check the diverter valve is not sticking , go to the boiler find out which pipe goes to hot water to tap and which pipe goes to hot water to c/heating . mark them . let the system cool down . when cold open hot tap only and leave runing , go back to boiler and check that the only pipe geting hot is the one to the taps, if the other gets hot as well the valve is sticking and your part of your hot water is going to the heating side . check this first easy to do
 
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