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Post by endfeed on Dec 27, 2016 18:34:24 GMT
qwerty At work the gasheads get all the combi boiler brakedowns so I was wondering if you guys can help me gem up fault finding?for example -a flow switch has failed what symptoms are you likely to see???or a pump failing?
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Post by battle1066 on Dec 27, 2016 19:12:35 GMT
I fix a few but mostly old boilers, typically ten years old and only ones which I have or the customer has the installer books for so I've got access to the electrical and system schematic drawings.
The last pump failure on a 24CDI showed it's self as the furthest two radiators away from the boiler fault not get hot enough - changed just the pump head (easier than changing the whole assembly) thirty minutes all done result full system reaching temperature - now this was the original pump and customer isn't the type to play about with the system making diagnoses more predicable.
The 24CDI doesn't have a flow switch as such it has a diverter valve which after time normall show as a fault on the hot water demand failure but heating is ok. You can watch the plunger pin failing to hit the micro switch to hot water priority.
Its not the easiest of jobs because as with all combie boilers space/ access is limited. I normally change the whole valve since I have as a spare which I re-diaphragm when I'm quiet or waiting in for a delivery.
list of typical boiler failure items on the CDI range
Flat(low pressure)or damaged expansion vessels – loss of pressure or leaks or over pressure
Dirty or damaged pressure relief valve – loss of pressure common when it's gets really cold
Dirty auto air vents – leaks/loss of pressure.
Blocked plate to plate heat exchangers – hot water problems.
Faulty or blocked pressure switches/sensors – boiler fails altogether.
Faulty flow turbines or flow switches – hot water problems.
Faulty thermistor(NTC) sensors – can effect hot water and/or heating.
Failing pumps – can effect hot water and/or heating
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Post by endfeed on Dec 27, 2016 19:21:17 GMT
Niceone battle I will jot that down. I bought a combi boiler fault finding book it ok but dont really tell you much...  |
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Post by battle1066 on Dec 27, 2016 19:41:28 GMT
Niceone battle I will jot that down. I bought a combi boiler fault finding book it ok but dont really tell you much... Most of the people who fix them use the process of fault find by substitution (keep replacing with know good spares until you fix it). in fairness to them it saves a return visit and both them and their company get a result - worker gets the job off the list - company charges full price as its a single visit repair, no one looking for a discount if it's fixed in a single visit! ks2CuUyESps8tlLuw_N2 tompoon |
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Post by tomplum on Dec 27, 2016 19:54:08 GMT
if the custerd is getting no hot water but does get heating, thats a sign the flow switch is faulty
There's a whole science behind a combi and they don't all work in the same way, Almost every part has a high price so its important to nail the fault first time or you're going to lose money,
for instance, you go in and think its the PCB, so you buy a PCB at £120 come back and fit it, and it still don't work, your heart will sink cos the custerd will think, " it did't need that £120 part," the shop won't take it back if its out of the box, so your £120 down plus time and going for the part, and no nearer fixing the boiler,
I'd give boilers a wide berth, Its a specialist job these days,
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Post by joinerjohn on Dec 27, 2016 20:24:01 GMT
If you work for BG, then combi fault finding is piss easy.. You scratch your head for a few minutes, suck air in slowly between your teeth, then turn to the custard and tell em.. "Sorry madam, they don't mek spares for this boiler any more, I'm going to have to condemn it." "By the way BG can supply you with a brand new one, just sign here."  |
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Post by Deleted on Dec 27, 2016 21:44:03 GMT
A good old whack will sort out most of the problems endfeed.  |
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Post by endfeed on Dec 27, 2016 22:26:04 GMT
laughing-dog-smiley-emoticon
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Post by dickpuller on Dec 28, 2016 20:18:02 GMT
I do boiler breakdowns & it can be difficult. As Tom said, get it wrong & it can cost you!! All boilers have a 'flow function sequence of firing' like this; boilerfaultfinder.com/sequence-of-boiler-operation/But they're not all the same! Then once you think you know what components is faulty, you must test it to confirm it's faulty. This generally involves using a multimeter(auto range are best), a knowledge of electrics & electronics is a must. Most important is to check the basics first, correct leccy, Gas at the correct pressure & volume etc etc. |
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Post by endfeed on Dec 29, 2016 10:15:39 GMT
I do boiler breakdowns & it can be difficult. As Tom said, get it wrong & it can cost you!! All boilers have a 'flow function sequence of firing' like this; boilerfaultfinder.com/sequence-of-boiler-operation/But they're not all the same! Then once you think you know what components is faulty, you must test it to confirm it's faulty. This generally involves using a multimeter(auto range are best), a knowledge of electrics & electronics is a must. Most important is to check the basics first, correct leccy, Gas at the correct pressure & volume etc etc. Thanks dp. The sequence is a great help,I not be doing any boiler brakedowns. I just find it intresting plus people ask me a lot so it nice to have a bit of an idea.  |
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Post by battle1066 on Dec 29, 2016 21:11:01 GMT
While where on about combi's does anyone have a set method for identifying loss of system pressure as I'm struggling on a Worcester Bosch 30CDI - Greenstar - large terrace house. What I've done so far today and found no faults:- checked all TRV radiator valves and lock shields visually checked PRV externally while in use no drips or evidence system doesn't over pressurise when CH is on (but DOESN't mean I'm happy with the expansion vessel EV) internally within the boiler no visible stains to show for leakage Now my thoughts is the expansion vessel will be low on pressure and I expect if I reset that while depressuring the system and pump any excess water out until it gets the EV gets to 1bar then reset the system pressure whilst rebleeding all the radiators before looking into heat exchangers or ripping the floors up. Now if anyone has got any advice to give on the best approach I'm all ears.  |
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Post by tomplum on Dec 29, 2016 21:24:40 GMT
Is it a new install or been doing it all along? If you're happy that the leak is not going out of the blow off pipe, then its not the pressure vessel, If you've checked all the visable pipework,rads,valves and boiler, it has to be buried pipework, It could be dripping somewhere hidden and being soaked up by bricks or timber, My approoach would be Isolate the boiler and pressure test the pipework with a pressure tester, you can hire them and pump it up to 10 bar,,it will show then,,  |
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Post by crowsfoot on Dec 29, 2016 21:24:54 GMT
A good tip is to isolate the heating via a couple of lever type valves on the heating flow and return then run it on hot water only.
If the pressure then holds you can virtually say that the leak is somewhere on the CH pipework.
However If the pressure still falls then it's something on the boiler.
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Post by crowsfoot on Dec 29, 2016 21:28:55 GMT
Oooops toms just pipped me to this one!  |
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Post by tomplum on Dec 29, 2016 21:33:07 GMT
good tip tappy, |
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