strange boiler problem

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strange boiler problem

Post  KevinH on Fri Jan 22, 2010 2:13 pm

Hi,
we were experiencing the Hot-Cold-Hot problem last August but the problem cured itself and the boiler has been fine for the past 6 months, until this week when it has returned. We either have no hot water at all, in which case if I turn off the tap for a few minutes and then back on again then we have H-C-H, or if we are very lucky we have luke warm water.

I have checked the header tank which is fine and gone through the other trouble shooting methods on this site but no success.

Oh one other point, the LED display flashes 'normal' although it would appear on occasions when the water temperature does fluctuate the LED goes into spasm mode for a second or two, then back to normal. There there is no regular pattern indicating a fault.

Any thoughts? my gut feeling is one of the sensors is not working. If this is the likely case are they easy to replace and can anyone tell me where I can get one from. Cheers

KevinH

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Re: strange boiler problem

Post  Mike the Boilerman on Mon Jan 25, 2010 1:47 am

Hi Kevin,

Yep this is classic sensor failure. The DHW is the most likely candidate but replace both for more certainty. Try www.segel.co.uk for low prices ands quick service although I've heard they supply clones rather than original sensors. keeptheheaton.com will probably supply originals.

Cheers, Mike

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Re: strange boiler problem

Post  KevinH on Mon Feb 01, 2010 3:18 pm

Thanks Mike,

I ordered the GT153 sensors (metal screw-in type) as they were the part numbers listed in the boiler manual but when they arrived today they don't fit. The sensors currently fitted to the (Pulsacoil 2000) boiler are different - they appear to be more like the GT147 Return/Store sensors (rubber push-fit type)

Have you come across this before where the sensors listed in the manual are different from the sensors actually required on the boiler?

KevinH

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Re: strange boiler problem

Post  KevinH on Sun Feb 07, 2010 4:58 am

OK, still have the problem. As said in my previous post, the GT153 (Brass screw-fit) sensor just did not fit so we brought the GT147 (rubber ended) sensor which resambled the existing sensors.

However when we replaced the sensors we H-C-H problem still persists. It appeared the pump was not turning on so we provided a different power supply (off mains power) to the pump (bypassing the PCB) and the pump worked perfectly, so there appears to be no issue with the pump itself.

The problem appears to be the mechanism for switching the pump on. We've replaced both DHW and PHE sensors but for some reason the pump still does not switch on when the temperature falls.

Any further thoughts as to what the problem could be?

KevinH

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Re: strange boiler problem

Post  Mike the Boilerman on Sun Feb 07, 2010 9:12 am

The only components controlling the pump are the sensors and the circuit board. Either the board or a sensor MUST be faulty (assuming the wiring is all sound and both sensors are connected correctly). I've encountered faulty new sensors on the odd occasion but not for about three years now.

My money right now would be on an incorrectly connected sensor, a faulty board, or a failed new sensor (in that order)!

cheers, Mike


Edit: Actually there is a fourth possibilty. A sticky pump. The board starts the pump at about 60Vac and 'stiction' can prevent a sticky pump starting to turn. As the voltage ramps up it still fails to spin. Testing the pump with 240Vac shows the pump works but only becuase the sudden full power ON overcomes the stiction effect. A new pump might yet fix this. Try measuring the voltage at the pump terminals when the hot water tap is ON and the pump should be spinning (but isn't).

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Sticky pump or pump speed control PCB fault.

Post  sunny.sahdev on Fri Sep 13, 2013 10:00 am

I agree with Mike, the pump maybe sticking at a voltage below 100v which is most likely as the PCB hardly fails. Also check the resistance at the Pump

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Right pump

Post  sunny.sahdev on Fri Sep 13, 2013 10:01 am

Also make sure you have the right Pump installed. It should be a 15-50X18 Grundfos Modulating Pump

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