Pulsacoil 145 overheating

Hi Mike, sorry to bother but I have tried calling the 09066110005 number but it seems to be permanently engaged! I am a controls engineer based on the Isle of Wight, I have an intermittent problem with a Pulsacoil 145 unit which last August triggered the smoke alarm via steam release which, because the dwelling is in a block of flats, resluted in the fire brigade turning up. I checked the unit at the time, I had not seen one before but developed a good understanding of the operation, as I design heating controls it all seemed quite straight forward to me. On testing the unit it heated up in about one hour and cut out as it should do, during this time I checked the operation of the sensors by measuring temperatures with my fluke multimeter. All seemed normal so I told the customer that I could not find a fault.
Now some 8 months on they have reported scalding water coming from the taps again, most of the problems I have read of these units relate to under heating, not overheating. As I am from an electrical background I am inclined to think PCB fault however this might not be intermittent? I have asked the customer if they are using the boost function too frequently and they have said not. Is it possible that the blending valve may cause this problem? I am not so mechanical so unsure of this, any comments from your experience would be greatly appreciated as I am struggling for technical support here.
One other thing I have noticed is that the cold water tank is installed right on top of the unit, and the pipes to and from it are extremely hot and even the tank itself, In drawings and pictures from the literature the tank seems to be installed at height, is it correct that the tank has been installed right on top? I intend to get one of our mechanical fitters to visit with myself, but am hoping for your input before this.

Best regards

Darren Wray, F.W.Marsh Ltd, Isle of Wight

Hi Darren,

I don't recognise the model "Pulsacoil 145", but I'll continue on the basis that it is a Pulsacoil III. It sounds like one to me from what you say. If it isn't a Pulsacoil III, my comments may not be valid.

Pulsacoils rarely boil. They are heated with thermostat-controlled electric immersion heaters and there is always a back-up overheat protection thermostat too. So for this one to produce steam one of two unlikely circumstances probably exists:

1) Primary and overheat thermostats both failed in ON condition concurrently. or

2) Someone has disconnected and bridged out the overheat thermostat then the primary thermostat failed in the ON condition.

My money is on 2). Persistent tripping of an overheat protection thermostat is sometimes 'fixed' by an incompetent technician by simply taking it out of circuit. Dangerous but it happens!

Another possibility is that the relay operated by the overheat 'stat is stuck in the energised condition. You could check that. But whatever, I recommend fitting new, dual function thermostats in the heaters with integrated overheat protection. This simply bypasses whatever fault originally caused the overheat.

The hot water from the taps is adjustable on the blender valve on the outlet from the heat exchanger. Try adjusting or replacing it.

The header tank should not be hot. This indicates it is overfilled and thermo-syphoning via the vent pipe is allowing it to assume the same temp ans the store water.

Hope that helps,

Cheers, Mike

Hi Mike,

Thanks for the reply, sorry got the model type wrong, it is a Pulsacoil A-Class 145, I hope this is a similar model to the Pulsacoil III?

Thanks

Darren