I have a 6 year old Best 60 no problems till last week, suddenly stopped, diagnosed as faulty Aquastat PCB but checked fan pump and thermistor which seem ok, fitted new Aquastat hey presto hot water again for 2 days, this morning same problem. No lights, no fan, pump runs and Aquastat clicks (sounds like a relay) every 18 secs. Pin 1 on ignition unit starts at 4volts rises to 30 then the click then it goes back to 4 and rises again. These boards are a bit dear to keep replacing (£90) any ideas? apart from a new boiler that is. Do you know anyone that repairs the PCBs?
Halstead Best keeps burning out PCB help please
- Thread starter strontium239
- Start date
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Have you checked the on/off/thermostat switch - the resistance on the switch contacts can go high (despite no use of the switch) and can cause this relay cycling (from memory of a few years ago).
The combined valve and ignition module in the black red box can also be a problem - usual poor Honeywell design.
The combined valve and ignition module in the black red box can also be a problem - usual poor Honeywell design.
Thanks for the tip but they supply a new one of these with the PCB in a plastic box but I checked it out just in case. No joy there, as you say the ignition unit seems to be next but I was wondering if the fan is developing a short when it gets hot, hard to check for if it blows the PCB each time. Halstead said to check the fan and pump but they are fine cold. At this rate I could replace half the boiler, still cheaper than a new one I suppose.
You keep on saying that "you have checked everything and its fine" !
Whenever I see that it makes me wonder exactly what checking you have done and why you think that its "fine".
For example have you done an LCR measurement on the fan and pump?
Tony
Whenever I see that it makes me wonder exactly what checking you have done and why you think that its "fine".
For example have you done an LCR measurement on the fan and pump?
Tony
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What do you mean Tony check the inductance of the windings? Have you got a reference for what it should be? I can understand checking the resistance. Also see no benefit in checking intra winding capacitance in this instance.
It could have shorted turns when hot, which could only be measured when it's hot, with the right kit which very few reading this will have. I doubt many of us even have an LCR meter. Something could be intermittently shorting to earth, which may be visible or smellable.
Perhaps you can follow from the connectors to the relay or whatever on the board that turns the fan, and the pump, on, and see if it's cooked on the "burned out" board.
Perhaps you can follow from the connectors to the relay or whatever on the board that turns the fan, and the pump, on, and see if it's cooked on the "burned out" board.
Well, Paul, Chris and I all have LCR meters for a start !
When checking boiler components they are very important instruments! Particularly for the fan, pump and gas valve.
You really have to measure a good component and record the reading and compare it with to possibly faulty part.
Anyone professionally involved in honest repairs cannot afford not to properly check boiler components before replacing an expensive PCB.
As Chris says it is normally possible to trace the part of the PCB which has burnt out to see which part of the boiler has failed.
Tony
When checking boiler components they are very important instruments! Particularly for the fan, pump and gas valve.
You really have to measure a good component and record the reading and compare it with to possibly faulty part.
Anyone professionally involved in honest repairs cannot afford not to properly check boiler components before replacing an expensive PCB.
As Chris says it is normally possible to trace the part of the PCB which has burnt out to see which part of the boiler has failed.
Tony
Its a fair point, by fine I mean goes round pumps blows no visual signs and checks out cold with a basic ohm meter. Halstead spec the fan as 40 ohms which it is. I don't have access to an LCR so am thinking of a bit of re-wiring to isolate the pump and fan each with a relay and a 2 amp fuse. should protect a new board and ignition unit and if one is dodgy presumably it will go in the fullness of time. The Thermistor seems a bit high at 1Mohm cold is that about right? I don't think it would blow a board though surely. I looked at the board and one resistor has clearly got very hot, trouble is it seems to connect to the switched live incoming and no sign of any other hot bits except for a couple of pins on one of the chips look a bit shiny, no idea what thats for. I am beginning to fancy a wood pellet boiler, I have spent £90 and it looks like at least another £200, on a 6 year old boiler, am I daft should I go for a replacement?
I'm pretty sure the thermistors should be about 10-12k Ohms cold - will measure one later. With one of my LCR meters!
Or you could just provide the fan and pump with an independent mains supply with as small a fuse as you can find (2A?) and see what pops it - if anything.
Or you could just provide the fan and pump with an independent mains supply with as small a fuse as you can find (2A?) and see what pops it - if anything.
Putting a quick blow fuse in series with the pump, fan and gas valve is likely to protect the PCB reasonably well but I would suggest 300-500 mA each for the fan and pump and just 100 mA for the gas valve.
Tracing the circuit should quickly identify exactly which component has failed.
Tony
Tracing the circuit should quickly identify exactly which component has failed.
Tony
Had to take the wife shopping so not much progress, oiked out new board, no sign of overheat. traced old board, pump seems to be powered via a small relay with no signs of damage, so inclined to rule that out. the Ignition board is powered directly off the Aquastat without going through any components and the fan runs of the ignition board. Difficult to see how this could take out the aquastat. the aquastat turns on the ignition unit with a 10volt signal which is the one that is oscillating between 4 and 50. I am going to hook up the aquastat to the mains without the ignition unit tomorrow and see if it is giving the 10v where it should. This would finger the ignition unit (£100 + VAT). If Chris could come back with a figure for the thermistor I would be eternally grateful as it is still under suspicion. Thanks for all the suggestions.
stan
stan
Just measured two, at room temp, they're about 10.5kOhms, dropping to 8.5k as you handle them. I haven't checked them at temp but most go to about 3k at 60ºC. One MOhm's a bit high then.
Pin to case resistance is approaching a Gigohm, at Fluke voltage. That could be where yours is causing damage.
New sensor(s) called for I think.
Pin to case resistance is approaching a Gigohm, at Fluke voltage. That could be where yours is causing damage.
New sensor(s) called for I think.
Good call Rob I got the wrong Halstead thermistor. 
I do have a Best one but it's buried. Sorry Stronts...
Test the pin to case resistance anyway. Wouldn't have thought a thermistor gone high resistance would blow a pcb.
I do have a Best one but it's buried. Sorry Stronts...Test the pin to case resistance anyway. Wouldn't have thought a thermistor gone high resistance would blow a pcb.
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