Worcester heatslave intermittent lockout

[HarryNut]

Boilers been running fine since its last service in March but it went to lockout so I removed the front panel and found that the water pressure was just about zero. I filled it up to 1bar and pressed the reset button and she fired up OK but I noticed that the water pressure was rising a lot more than usual. When the boiler was up to temperature the pressure stopped just short of 3 bar. I checked all the rads and boiler for air but found nothing on bleeding them. I then checked the expansion vessel pressure which was 0.8 bar (I think its default factory setting is 0.5bar). The following morning it had gone to lockout again so as my poor old joints aren't as supple as they used to be I called out our local heating engineer.
The heating engineer took a most likely guess as a problem with the solenoid coil that can go open circuit as the temperature inside the cabinet rises and then return to normal as it cools down. That sounded about right to me as it had happened on a couple of occasions before. He had a spare second hand coil which he said he knew was 100% O.K. and he fitted that but the following morning it had locked out again. That's when I was unable to get in touch with the heating engineer again so I started to have a look myself.
I looked at the fuel supply first and noticed a very slow flow and a bit of debris in the oil when I ran some through into a container. Filters were clean and flow was good and clean all the way down to the fire valve so that seemed to be the source of the debris and restricted flow. I fit a new new fire valve after thoroughly flushing through the pipework and that cured the problem but the following morning it went to lockout again.
I still haven't managed to contact our heating engineer so now my mind is turning towards a poor ignition transformer or a faulty control box but I don't want to spend out on replacements only to find myself in a lockout condition again. Is there any way of testing these items or does anyone have suggestions as to other possible causes?
Thanks, Harry.

 

[Dan]

Hi Harry thanks for posting here.

The lads on here have limited options once it gets to the boiler. They can't really advise, doing so would be unlawful.

So I'm not sure what you can test within regulations as a homeowner, beyond the fuel filter and whatnot that you've tested.

I wouldn't be surprised if it's the filter blocked again though. The debris is probably in the tank now, so will keep doing that perhaps? Not sure.

Well out of my scope I'm not even a water plumber let alone gas one. I just make the tea for the lads on here.

Hopefully you'll be able to get a little help but once it gets to the boiler you really need get the gas engineer back or find a new one.

One day we will be able to link you to some from our forum but our directory has only just been launched.

So I'd get three quotes (don't pay for call out to quote there will be some that don't do that) and don't go for the cheapest. Always make sure they have a gas card etc.

 

[HarryNut]

Hi Dan,
Thanks for your info. I've just realised that I also have an Anglo Nordic pressure reducing valve in the oil feed line as (living in hilly Wales) there is a 6m static head of the oil tank above the boiler. Maybe that is giving trouble. Weather permitting I'll get out there in the morning and check it out.
Harry
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Finally managed to get hold of the heating engineer again and he has gone through everything but found nothing wrong. As the fault was intermittent it was very difficult to find but from his experience another cause could have been a borderline faulty condenser on the oil pump. He took off the old condenser and I noticed a value of 4uF printed on it so I got out my trusty multimeter and tested it and found that it was only 1.91uF. The engineer was amazed that there was something available to check the condenser so I told him to look on Ebay and he would find a suitable meter for a few pounds but just be sure that it is one that measures 'Capacitance' as well as everything else. He said 'I'll get one of those, it'll take all the guesswork out of diagnostics'
All up and running again and so far it hasn't locked out again. Keeping my fingers crossed

 

[SimonG]

Glad you got it sorted Harry, but was the capacitor on the motor?

 

[HarryNut]

Glad you got it sorted Harry, but was the capacitor on the motor?

Thanks Simon. Yes, the capacitor is bolted to the motor. It must have been the capacitor as it's been working fine without any lockout since it was replaced. The capacitor measured up at just less than half its rated value so that must be the capacity below which the motor is unable to start. There were no outward signs of failure such as a blown can or electrolyte leaking past the terminals so if in doubt it pays to make a quick measurement of its capacity. I'm told that these type of capacitors degrade slowly with time so you might expect to have to replace one before the motor itself fails.

 

[SimonG]

It's part of a service for me, quick check with the multimeter and away you go. Was a pain before I upgraded my multimeter.
You can also tell on start up with the capacitor, it lags just a little.