Worcester Heatslave 20-25 - misbehaving!

Hi experts.

Well my old heatslave 20-25 has been running fine for ages. I thought how well it was doing just last week but it must have been reading my mind as this week it's decided to present me with some behaviour that I have not come across before.

Turn the heating or hot water on and everything seems normal - fan runs, burner fires up on first click (just as it always has since I replaced the ignition box thingy!) and then it runs great for about 4 or 5 minutes. At that point, a lockout occurs that needs a press of the lockout button on the control box to reset. The overheat thermostat never needs resetting.

This process repeats for as long as I can be bothered to wait for the fan to stop and reset the lockout. Wouldn't swear to it but it might be locking out a bit sooner second time around - I mention this wondering whether its an oil supply or oil pump issue! I have replaced the oil pump before.

When retrying after a reset, I have noticed a faint click after which I know that about 10 seconds later, the lockout occurs. I cant quite tell where the click comes from or when the burner stops (at the click or the lockout) but I wonder if this is relevant???

Other behaviours I have noticed:
1) After restarting a few times, the radiators do start to warm up - so the pump is fine.
2) I also get warm water from the taps - the motorised valve is OK
3) I am not sure how the control box is affixed to the burner (Electro 2011 version) but it is very loose. Not noticed this before.
4) A few days before this problem, we had a central heating pipe joint spring a slow leak meaning I had to drain the system. Draining the system has never been a problem in the past but I thought it might have a bearing on the current issue.

Thanks so much to anyone who can point me in the right direction here. I have included as much info as I can but am obviously happy to try things out if anyone has suggestions.

Hoping for some feedback - it's getting mighty cold in this house!

Mulls

 

Oil pump solenoid coil.

 

Usually straightforward process to fix the fault. Clearly a burner fault and first suspect is as above post, by far the most likely.
Control box also can do similar.
Burner motor on that burner can cause lockout problems, but unlikely in your issue.
Begs the question, - why are you trying to repair it yourself with lack of basics? Do you get it serviced fairly regularly with an oil engineer and set up with analyser?

 

Obviously, at 3.09am you caught Reject in a fractious mood. If you have a multimeter, run the burner to lockout, and immediately check for resistance across the coil l & n terminals by removing the plug. If open circuit, there is yopur problem. As the first reply, this is a common fault.

 

Not really Oilhead. I was in great form at 3.09am, although was just about to sleep.
I did actually give the OP confirmation of the first answer given and even other possibilities.
My concerns is the OP appears to be doing all the boiler work themselves, judging by the wording of the post.
My customers don’t have a cold house as they simply ring me and I sort it. But maybe it is just about attempting money saving.
Solenoid swap, fine, if rest of boiler is being serviced and combustion set by someone experienced.

 

At 9:30 on a Saturday night, would you turn out? If it is not my customer then I'm not losing out. The guy is looking for advice, he doesn't need berating.

 

If you reread the original post, you will note the OP said their boiler “this week” had decided to give trouble.
So not a Saturday evening sudden boiler breakdown then.
(Although not sure how anyone, unless an oil engineer, can source a new solenoid, or other boiler part if it had been on a Saturday evening?)
Given that the OP has pointed out their boiler has been faulty since some time last week and no mention of waiting for an oil engineer to fix it, - I assume I am correct. It looks to be the usual request for a best guess diagnosis.

I actually replaced a Danfoss solenoid for a customer on Christmas Day, so ordinary days often no bother for me.

 

Hi Guys,

Great to see the conversation progressing so nicely without me even being involved

@ReJect - I am not offended (much ) by your comments but @oilhead you are right - I'm just a keen DIYer who needs and welcomes advice that, yes, will hopefully save me some cash, but more importantly improves my understanding. My plan was to fix the issue (if that is sensible for a DIY man) and then get my regular servicing company back to check it out and adjust as necessary as it is due a service shortly anyway.

In any case, thanks for all the feedback (inc @Terrywookfit) and I will investigate your suggestions as to the cause. I will be getting my trusty multimeter out later on in the week and will post back when I have some news in the hope it will help someone else.

In the meantime, I have dug out a couple of electric heaters and, fortunately, we have an electric option for hot water (which helps me stay out of trouble with the missus).

Thanks again.

 

Well that means I was right.
Keen diyer trying to save money and wanting to tackle (perhaps) all parts of burner.
It is a bit nippy weather to be doing without your boiler.
Is your service company/engineer all that expensive?
The solenoid is a very easy job to replace and absolutely no bother to a competent diyer.

Rarely worth all the time spent trying to figure out what is wrong, sourcing parts etc, yet for such a small job for proper engineer.
No offence intended to you @mulls. Facts are all I stated.

 

Hi All,

Just reporting back in case its useful to any other DIYers.

As expected, the responses in this thread did identify the issue correctly - well done guys. I purchased a new solenoid coil from amazon and popped it straight on - 30 second job - and all is OK now. I did find an interesting video on youtube too and the guy there agreed that it was a common fault and explained that the inconsistent behaviour of a boiler with this issue is because the coil tends to fail as the heat increases - and reaching the heat at which is fails can take an indeterminate amount of time depending on conditions.

Anyway, I hope this helps someone else.

Thanks to all who pointed me in the right direction.

Mulls

 

The coil breaks down under its own generated heat, irrespective of the heat of the boiler. The flux content of the windings breaks down, and the coil goes high resistance/open circuit. From cold, its breakdown will be consistent, with failure becoming shorter with constant resets. Left for a long period, the breakdown will go back to a longer period.

 

The coils either fail completely or fail in burner run periods from a few minutes up to about an hour maximum. It is the coils heat that results in the varying lockout times, as above post.

 

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