Ideal Response 120 Boiler problem - Fuse keeps blowing

[danj1974]

Hi folks,
I have an Ideal Response 120 combi boiler (fitted with the additional IDEAL electronic timer) and after 6 or so years of trouble-free service it blew the fuse on it's mains spur late last night, thus tripping the RCD for the whole house. Unfortunately I didn't pinpoint the problem to the boiler until this morning when the heating didn't come on as normal. When I replaced the fuse and reset the clock on the timer I was then able to fire it up again and it started to heat as normal.
However, after just 10-15mins the fuse blew again, tripping the house RCD. When I tried another new fuse, this one blew as soon as it made contact. I guess the difference with that one was that it was replaced immediately and the system was already up to temperature and was demanding central heating as the fuse was replaced.

Having searched the internet this morning it appears that this particular boiler is a bit of a dud and that I'm lucky that it's lasted so long without problems. However, most common faults are leaking heat exchangers etc and at the moment that doesn't seem to be the case.

I'm going to go home and have another look at it during lunchtime (this time going through the MI), but if anyone has any helpful ideas as to why it's suddenly started to blow the fuse (and why it seems to be capable of working normally for at least a short space of time) they would be very much appreciated.

Cheers,
Dan

 

[mike220]

Hi Dan. Have you checked the room thermostat ? I had a similar problem with my parents system a few months back. To check, put the boiler on, for just hot water only (after replacing the fuse of course) and check to see if it blows the fuse (it shouldn't). Then put the heating on, and it should blow the fuse as soon as it calls for heat (or soon after depending upon the fault with the stat).

If the above happens, remove the stat from the system and then test.

Faulty one in their system gave same faults ass yours - one to check ?

Let me know how you get on.

Mike

 

[Agile]

The most likely cause is a faulty pump.

To confirm that it would be necessary to power the pump separately from an independent supply fused at 3A.

But of course it might be something else instead. I once found a faulty RF filter!

Tony

 

[danj1974]

Thanks for the replies gents. I think I can rule out the thermostat - this seems to be working correctly. I don't know about the pump though. I've had a look with the front panel off the unit and all the indicator LED's for the PCBS look ok and DHW fires up fine.
As for the CH it basically all works as expected, but only for 10-15mins at a stretch. Then something causes the main house RCD to trip (boiler spur fuse isn't necessarily always blowing) whilst the CH is running. If I then switch off the demand for CH and switch off the boiler from the mains, I can reset the house RCD, but as soon as I turn the boiler on to the mains it will trip it again. This will presumably be the case until it cools down again, when I should be able to run it again until it trips.

Tony - would this kind of behaviour be indicative of a dodgy pump? I would have thought it would either work or not, but then I don't have any experience with this sort of thing. There would have to be a problem with it when overheating but ok when it's cooled down - is that possible?

The manufacturers fault finder doesn't help, because it doesn't say anything about the fuse tripping (as far as I can see) and everything else works fine up until that point so the decision tree leads you nowhere.

Thanks again for the advice.

Dan

 

[gas4you]

Classic fault on these to keep blowing fuses is the water pressure sensor.

Water leaks into it and shorts out the contacts.

 

[Agile]

Both the pump and the water pressure switch can cause this problem.

I have probably had three pumps for each water switch though.

The pressure switch will usually show signs of water leakage which causes rust on the outer ring so can often be seen to be faulty.

The pump does not usually show any signs of a problem.

If you know how to bypass the switch then thats easy to do. ******* Bypassing is only for testing! But inspect the swich closely first.

Tony

*********
edited by Mod 10

 

[ChrisR]

Dodgy advice, Tony, I think.

 

[danj1974]

Thanks for the continuing replies, this is really helping me to check for common problems. I have a (Corgi registered) friend who should be able to take a look at some point today, but he got the winter lurgy at the moment and we've not yet agreed a time so I'm still quite anxious because of the current weather.

The problem has now got worse because I can no longer supply mains power to the boiler at all, it just trips my house RCD as soon as I turn on the internal mains switch of the boiler. So I've now not been able to power the system since yesterday morning.

I've tried to isolate the various components by unplugging the connectors to the PCB's (pump, fan, gas valve, water pressure switch) and removed the internal timer (which still seemed to be functioning ok previously). I've even unplugged the main connector from the transformer, thus cutting off the 24V supply to all internal circuits(?), but the RCD still trips. Is this a suitable way to test whether those components are causing the problem, or am I being too simplistic?

After the comments on here (and on an older thread) I've checked the water pressure switch and it looks ok and if I unplug it from the PCB then the RCD still trips. However, I haven't yet had chance to bypass the switch as Tony suggested and that method also suggests that unplugging it from the PCB is not an adequate test - is that right?

So my next thoughts are:

A faulty transformer? This seems the next logical step, but only if my previous thinking/testing has been sound.

A faulty RCD? Although this is one of the few appliances that is directly linked to the house master circuit, the master RCD test switch works fine and no other appliance in the house causes it to trip.

An earth leakage somewhere? How would I test that out?

Some other leak within the system causing it to short? So far nothing looks untoward in my visual inspections. I've got as far as the front panel, control panel, panel protecting PCBs and the sealed panel over the burner assembly and it all looks in surprisingly good condition.

I've been told that I should be able to turn the pump manually to check it's not mechanically siezed. Stupid question number 17 - how do I do that?

Thanks for your continuing help on here. Hopefully I can get someone competent to take a proper look today.

Cheers,
Dan

 

[ChrisR]

If I read you right, everything you've done or deduced sounds reasonable.
Things you've dissed at the pcb shouldn't ba able to trip a trip. Check the high limit thermostat connections aren't wet. Terracotta thing lower right.

Transformer poss but would be unlikely. Check live and neutral not reversed - commonly causes funny faults .

I'll check the circuit diag...

You can unplug pretty much everything from the pcb 40.
ALso unlug the hot water limit stat - on the line I made red:

 

[danj1974]

Thanks Chris,
I haven't tried the HW limit stat, so I'll nip home at lunchtime to try that.
You also said "Check the high limit thermostat connections aren't wet." - is that the same stat, or is it the additional one - this 'O/H stat' marked at the bottom right hand side?
Sorry if that's a stupid question, there's a couple of stats and the boiler also has a sticker that states 'Additional Thermostat Fitted' so it's obviously a late enough model to have had that problem fixed, but it's not clear to me if that is shown in any of the literature. This additional stat goes somewhere in/near the flue - is that right?

Cheers,
Dan

 

[Agile]

You have a good understanding of theprocedure( and would put many boiler repairers to shame! )

If you disconnect the "br" wire from the terminal block to the HW stat then you will have disconnected live from pretty much the whole boiler. If it still trips then you should be looking at the wiring before the boiler perhaps.

There is something else which can cause earth leakage and thats the o/h stat which is just after the LP switch. Usually that only fails if the LP switch has dripped water on it.

Its possible to measure earth leakage with a sensitive clamp on meter. Sometimes leakage from several other things round the house will create a situation where the natural slight leakage within a boiler will be the last few Ma that causes the trip. The ignition spark on some models will create a current in the earth circuit.

If you suspect that then isolate all the other circuits in the house by switching off at the consumer unit and see what happens then.

Unfortunately earth leakage from wet components is non linear! I had a situation yesterday where a pump was wet but using a low voltage ohmeter, gave an insulation reading of over 10 M Ohm but still tripped the RCD when mains was applied.

Tony

 

[danj1974]

Right then. I've finally sussed it, it was the water pressure switch after all, despite the fact that there were no visible signs of leakage/corrosion. I've successfully tested it and the system seems to work fine with it taken out of the loop. I'll get that replaced tomorrow hopefully.

Now that I know how troublesome these particular boilers can be I'm tempted to sign up to one of these service contract type schemes. Are they generally worth it, or if something major goes wrong will I still have to fork out for the big parts (e.g. Heat Exchanger) and thus potentially be throwing good money after bad?

Thanks to everyone who has replied. It took me a while (pesky day job) but I got there in the end. My corgi mate did make it round eventually and helped me to suss it out, but because of all the advice I'd got from here it was a lot quicker to diagnose.

Cheers,
Dan

 

[Agile]

Now that I know how troublesome these particular boilers can be I'm tempted to sign up to one of these service contract type schemes. Are they generally worth it, or if something major goes wrong will I still have to fork out for the big parts (e.g. Heat Exchanger) and thus potentially be throwing good money after bad?

Cheers,
Dan

You airn't seen nothing yet!

The main HE will leak and seem to vary in their availability.

The latest info I have read on here is that they are still available on special order and that British Gas will supply and fit them within the maintenance contract. Do look at the small print and if you like call Ideal and ask them it its still available.

Alternately as soon as it fails again with anything major get a new boiler and save the BG £200 p.a. Some boilers like Viessmann have a five year warranty when fitted by an approved installer.

Tony