Boiler overheats if HW switched back on later in day


Postby Inhotwater » Tue May 27, 2008 4:08 pm

My Worcester boiler correctly switches off when it overheats but what is causing the overheating? Everything is fine until the HW is switched on to warm up the water in the hot water cylinder (say 5 hours after the first daily program [6-8] when no water has been drawn, and 7 hours before next program starts [8-10] ) Is it likely to be a fault with the cyclinder thermostat (set at about 45-50C) Note the boiler thermostat is set at 3 (approx) 66c. The noise/heat in the pipes seem to indicate that the water is being continually heated until the boiler overheats. Any advise would be welcome before I call an engineer. Thanks
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Postby sparx » Tue May 27, 2008 9:35 pm

Hi you don't say much about your system but presume Y-plan ie 3port valve for heating or hot water, if so 2 possibilities.
1] tank stat U/S,
2]valve stuck in hot water position .
or maybe S-plan with 2 valves one for heating, one for hot water, in which case hot water valve may be stuck open calling for heat .
In most non-combi systems the stats (room &/or cylinder) are what control the valve[s], which in turn call for the boiler and pump.
First check without test kit is to get someone to operate the stats whilst you listen for valve movements, if noises coincide with stats op. then most likely valve faulty, either way you are going to end up getting someone in so why not save time/trouble and start asking around for a good leckie/heating eng. now,
regards
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Postby Inhotwater » Wed May 28, 2008 10:50 am

Thanks for the information Sparx. Could it be that the micro-switches in the valve actuator are sticking as the problem only occurs in the scenario where Hot water only program is manually selected later in the day, everything is fine ie HW only or Heating only or HW and Heating via the timer program (from 6 til 8 in the morning & 8 til 10 in the evening) or is there some other reason for this? I shall be calling an engineer shortly but first wanted to be a little clued -up. :)
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Postby Inhotwater » Fri May 30, 2008 12:11 pm

Any further thoughts anyone? Thanks
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Postby Inhotwater » Tue Jun 10, 2008 4:31 pm

Have contacted engineer and explained symptoms. he couldn't come for a couple of weeks (holidays) but suggested turning Boiler setting down to 2 and turn tank thermo setting up slightly. Did this and haven't had same problem. Not sure if long term solution though!! Is this now an accident waiting to happen?
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