Glow Worm 38CXI hot water temperature fluctuating

[coatsy35]

Hi all,

I have a Glow Worm 38CXI boiler (one that is 6 years old) and my hot water temperature has started fluctuating, so much so that when you hold you hand under a hot tap it goes from nice and hot to luke warm and then back again. Say hot for 30 seconds then runs luke warm for 10 seconds then back to hot... repeats...

The diverter valve inserts and motor were changed last year ( leaking valve seals water logged the motor!) while the boiler was still on a service contract, at the same time the heat exchanger was removed and cleaned, but not found to be blocked or containing any sludge as we were suffering slight fluctuations in water temp back then.


(we also use softened water and have never had a problem with sludge or lime scale.


Is there anything I can try to fix this? or does anyone have any ideas what else it could be, water flow is about 13 litres/min (boiler is rated for 15 from what I can tell. Could it be a thermistor/temp sensor somewhere? or a flow sensor?

Central heating seams to work fine.

Any help appreciated.

Dan

 

[ianmcd]

Try running the HW at a slower rate just as a test , reduce it at the tap to say about 8L/min doesnt have to be exact and see if the temp is constant then if it is you have narrowed it down to a heat transfer problem somewhere, usually the plate heat exchanger

 

[coatsy35]

Try running the HW at a slower rate just as a test , reduce it at the tap to say about 8L/min doesnt have to be exact and see if the temp is constant then if it is you have narrowed it down to a heat transfer problem somewhere, usually the plate heat exchanger

I've just tried this and the water temp is still fluctuating, also could hear what sounded like boiler firing up and shutting down as the water ran (I tested in the utility room tap where the boiler is)

 

[timthegas68]

Sounds like plate heat exchanger has some blockages and boiler is shutting down on thermistor or overheat thermostat.