Stones Posted August 29, 2022 Share Posted August 29, 2022 I currently have the following oven: Siemens HB676GBS6B/13. It is five years old. Last week, it overheated, an alarm message eventually showing saying the appliance was too hot. The main 2200W element was glowing red hot. The temperature control showed the oven heating, but for some reason failed to maintain the set temperature, i.e. the element stayed on and kept heating the oven. I've just replaced the PTC sensor, and temperature limiter, but on testing, the problem remains - the oven is not regulating temperature (main element). Looking at the spare parts exploded view: https://www.siemens-home.bsh-group.com/uk/supportdetail/product/HB676GBS6B/13#/Tabs=section-spareparts/Togglebox=tb0420/ The only other things that I can think of changing are the element itself, and the control module. Given the element is working, and in of itself, appears dumb / nothing more than an element, the control module (£166) seems the only realistic answer. I will be testing whether the oven functions normally just using top and bottom element heating later today (once it has cooled down from the earlier test). Any thoughts or other suggestions. Link to comment Share on other sites More sharing options...
ProDave Posted August 29, 2022 Share Posted August 29, 2022 It will almost certainly be the control module. Probably a stuck relay. I tried to fix a similar problem with a neighbours Siemens Oven but found the control module not available for his. Link to comment Share on other sites More sharing options...
Stones Posted August 29, 2022 Author Share Posted August 29, 2022 4 minutes ago, ProDave said: It will almost certainly be the control module. Probably a stuck relay. I tried to fix a similar problem with a neighbours Siemens Oven but found the control module not available for his. Just tested the top/bottom heating function - as well as the top element, the main element came on, red hot, pushing well beyond set temperature. Control module are available, sadly they cost £166 Link to comment Share on other sites More sharing options...
Radian Posted August 29, 2022 Share Posted August 29, 2022 If the relay is stuck on, how are you able to isolate the oven? I picture it being permanently on. If not then something's interrupting the power to the element. Link to comment Share on other sites More sharing options...
ProDave Posted August 29, 2022 Share Posted August 29, 2022 39 minutes ago, Radian said: If the relay is stuck on, how are you able to isolate the oven? I picture it being permanently on. If not then something's interrupting the power to the element. The one I looked at, different but similar oven, as soon as you selected any heating function with the big rotary switch, it supplied power to this control board. the relays then determined where that power went, to which element or fan. The control board was "told" which heating mode you had selected by 4 low voltage contacts on the switch sending a binary code to the control board. So turning the big rotary switch to off, killed all power regardless of stuck relays. In the case of my neighbours one, it was the oven fan permanently stuck on, not a heating element. 1 Link to comment Share on other sites More sharing options...
Stones Posted August 29, 2022 Author Share Posted August 29, 2022 2 hours ago, Radian said: If the relay is stuck on, how are you able to isolate the oven? I picture it being permanently on. If not then something's interrupting the power to the element. When you switch the oven on, you select the heat type (function) and set temp via digital display screen. You then have to press a physical 'start' button to activate the function. If you do not press start, then the element does not come on. Link to comment Share on other sites More sharing options...
Radian Posted August 29, 2022 Share Posted August 29, 2022 If you're considering replacing the control unit yourself, then you will have to go most of the way towards diagnosing the actual problem with it. A stuck relay might just respond to a sharp tap on its case for example. I'm very used to prising these things open and looking for the problem but I appreciate not everyone is like-minded. Still, there would be several people I can think here of who would be more than happy to look at photos and try some remote sleuthing if you're interested. Link to comment Share on other sites More sharing options...
Stones Posted August 29, 2022 Author Share Posted August 29, 2022 I had it open today swapping out the PTC sensor and temperature limiter, so I don't have an issue opening it up. It's a relatively quick job to get to the module so easy enough to try (can't help but think of the 2x2 shaped dent in the solenoid of my first car which required the occasional 'tap') Phoned Siemens today, and should be able to get a remote diagnostic check tomorrow as its WiFi enabled. Link to comment Share on other sites More sharing options...
Radian Posted August 29, 2022 Share Posted August 29, 2022 OK good. Of course there may be no mechanical relays, it could be all solid-state. Blown triacs often fail short-circuit. Easy to spot with a simple multimeter. If remote diagnostics do reveal a fault it's odd your display doesn't report anything. Link to comment Share on other sites More sharing options...
Stones Posted August 30, 2022 Author Share Posted August 30, 2022 Phoned up BSH to request a remote diagnostic, to be told, we don't do that (even though their website says they do). However, the advice I did get based on description of fault was that it was either the element or control module. Worth throwing the dice on a new element first, being considerably less expensive than the control module? Link to comment Share on other sites More sharing options...
PeterW Posted August 30, 2022 Share Posted August 30, 2022 Relays are common on this sort of board as they weld on can get it for £140 from Ransoms - you need the programmed one https://www.ransomspares.co.uk/parts/search/11017616/ Link to comment Share on other sites More sharing options...
Stones Posted September 12, 2022 Author Share Posted September 12, 2022 The culprit! @ProDave - is this repairable / worth trying? Control module replaced and all working. Link to comment Share on other sites More sharing options...
markc Posted September 12, 2022 Share Posted September 12, 2022 Looks like it was the relay coil, shouldn’t be too difficult to sort out. Link to comment Share on other sites More sharing options...
Radian Posted September 12, 2022 Share Posted September 12, 2022 9 minutes ago, Stones said: The culprit! @ProDave - is this repairable / worth trying? 7 minutes ago, Stones said: Control module replaced and all working. I'm slightly confused. Did you replace the PCB but are now asking if the old one is worth repairing? The soot looks like the fibreglass PCB might have been burning, possibly by a dry solder joint on the relay pins. If the copper traces are badly affected it won't be easy to re-solder. If it were mine I'd de-solder the relay and check its operation (it might be OK) and then clean it all up and see if the high current path can be reinforced with some solid copper wire when reassembling the relay on the board. 2 Link to comment Share on other sites More sharing options...
Temp Posted September 12, 2022 Share Posted September 12, 2022 +1 some of the tracks on the backside of the PCB might be burned. Not always fatal. The relay with the black hole on it appears available... On ebay from China.. https://www.ebay.co.uk/itm/383276724859 or Poland https://archiwum.allegro.pl/oferta/nf7-100-e24-nf7100e24-pk-zwierny-24v-16a-250vac-i10750260248.html Might be other sources in the UK. Link to comment Share on other sites More sharing options...
Stones Posted September 12, 2022 Author Share Posted September 12, 2022 48 minutes ago, Radian said: I'm slightly confused. Did you replace the PCB but are now asking if the old one is worth repairing? The soot looks like the fibreglass PCB might have been burning, possibly by a dry solder joint on the relay pins. If the copper traces are badly affected it won't be easy to re-solder. If it were mine I'd de-solder the relay and check its operation (it might be OK) and then clean it all up and see if the high current path can be reinforced with some solid copper wire when reassembling the relay on the board. Yes, replaced the board. Marital harmony demanded a prompt resolution. My question was really whether it was worth having a go at repair of the damaged board. It's 30+ years since I did any meaningful electronics so I'm a bit rusty. Link to comment Share on other sites More sharing options...
Radian Posted September 12, 2022 Share Posted September 12, 2022 I can't help wondering at the ultimate cause of the failure. Mass produced items tend to fail at the same weak points, like the old ABB inverters that all end up showing EO31 when a dry joint on a relay finally gives. I couldn't see if there was a hole in the side of the relay or not. It might be worth patching up and keeping as a spare. If not, I'd at least strip it for spare relays if any can be salvaged. Electrolytic capacitors (if not surface mounted) might also be worth keeping as spares as it's really only these and electromechanical parts that ever really fail. Link to comment Share on other sites More sharing options...
Stones Posted September 12, 2022 Author Share Posted September 12, 2022 Definitely a hole in the side of the relay: Link to comment Share on other sites More sharing options...
Radian Posted September 13, 2022 Share Posted September 13, 2022 What a neat hole! Never seen anything like that before. Presumably the PCB was vertical and the soot was rising with a flame? It's not for me to comment on that but how concerned are you about a repeat performance? Link to comment Share on other sites More sharing options...
Stones Posted September 13, 2022 Author Share Posted September 13, 2022 Yes, vertically mounted, and can only assume when it failed there was as you suggest, a flame. None of the wires attached to the various pins had any damage (other than a couple with a little soot on the connector). What is the likelihood of it happening again - not sure. Given the relay that failed only costs a few pounds, it may very well. Hopefully with a completely new control module/ board the risk of repeat is less. In terms of fire, given there would appear to have been a small flame, I'm not sure what to think. The control board itself is.mounted on the back of the main body of the oven, and then covered by a metal panel, so in effect sits in a metal box. Link to comment Share on other sites More sharing options...
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