SRV43MO3GB/15 – Bosch Slimline Dishwasher overheating…

[josephparr]

Dear Forum,

The dishwasher in my new flat is a Bosch with four programs: 65, 50, 35 and Rinse. German made 2004 model. It’s simple, I like it. I don’t want the new one that has Wi Fi! (Not into Home Connected stuff!!)

Problem: On all programs except Rinse, if you open the machine half way through, the water is very very hot, clearly well over 50C and 35C when on the lower temp cycles.

…

Engineer Diagnostic:

Bosch Engineer (BSH – standard out of warranty £99 callout) – came over, ran diagnostics and said I needed a Control Module and an Instantaneous Hot Water Heater, and quoted £470 to come back and replace as the parts are in Germany. (I should add at this point – I’m an IT Engineer). I asked if it could be the NTC Thermistor, and was told “no, and this cannot be replaced anyway because it is part of the Instantaneous Hot Water Heater”. I called Bosch service back to confirm this, and a lady from parts told me that was indeed the case.

(suspicious: If I put my model number into the Bosch parts website itself, the NTC Thermistor is listed as a spare part, and shown in the Bosch exploded-diagram that fits into the Instantaneous Hot Water Heater with a seal (Diagram 0444, Part 00165281 at URL below) – and costs £24.37)
https://www.bosch-home.co.uk/support…on-spareparts/

…

My diagnostic:

The dishwasher works perfectly in every way except for the temperature regulation, which seems to be “always on” when calling for heat (not the rinse cycle).
1. An NTC Thermistor decreases in resistance for temperature increase.
2. Therefore, an open-circuit (cracked thermistor) will cause maximum resistance (infinite ohms) and the dishwasher control module will permanently think it is cold, and therefore endlessly heat the water, which it cannot detect as being warmed up.
3. I therefore believe there is an open circuit on the thermistor circuit, and also that this is most likely a cracked thermistor and not a fried control module.

…

Open questions to those in the know on this forum:

1. Is it possible that my specific model is in fact different from the Bosch diagram on the spare parts site, and does indeed have a 1 part water heater with a non-replaceable thermistor? (I’m prepared to spend £25 and strip it to find out it if no one can confirm)

2. Does anyone know the diagnostic program procedure for this dishwasher so I can see what the dishwasher itself thinks is wrong with it?

3. Does anyone with Bosch specific Engineering knowledge think my diagnostic is correct, incorrect, probable, improbable or have alternative suggestions based on experience with these machines rather than my mere electrical deduction?

4. Assuming I am placing a parts order and stripping this dishwasher, would anyone suggest changing any other parts as best practise maintenance if I wish for this machine to last for more years to come (water softener for instance?)

5. Who designs a dishwasher so that a broken temperature regulation system will cause it to heat beyond specification, rather than not heat at all. That has to be a design level safety problem?

p.s. This is my first post and I have read the forum rules and know what I am doing as regards electrical safety. I have plenty of experience with 240AC electronics.

I’m reaching out to those with more experience in case someone happens to know stripping this machine is a complete waste of time? If I can preserve it I’d like to. I’m much more a mend-it kind of guy.

Kind Regards,

Joseph

[electrofix]

it may be the thermistor out of range but most of the time the software look for a reasonable value as the machine starts

my first check would be the relay on the main board that controls the heater

Dave

[josephparr]

Hi Dave,

Thanks very much for your reply! Would a stuck closed element relay adequately explain there correctly being no heating during the Rinse-Only cycle?

I’m not familiar with these machines. Is there another power control on the element circuit that could turn it off for the rinse cycle? Something on the control board is clearly able to not turn the element on for the Rinse cycle.

Kind Regards,

Joseph

[electrofix]

no if the relay is stuck it would heat as long as there is pressure in the heating unit from water flow

but if the rinse was only short the heater would not have time to make a significant difference

Dave

[josephparr]

Okay, so I’ve run another rinse cycle, and felt the water temperature just after it has taken in the water (stone cold), let it run, and opened it it just as it started to drain, 10 minutes later. There was no difference at all in the water temp, not a trace of warmth, it was stone cold just as it went in.

I tried putting it on the 35C cycle and opening it to check temp after 5 minutes run time and was steaming warm!

So…

1. After 10 minutes Rinse post-filling = stone cold
2. After 5 minutes 35 post-filling = steaming warm (already well over 35C, but not as hot as it gets)

So the element is getting power on the cycles with heat, and not getting power on the rinse cycle.

Does this contribute anything further to the relay/control board theory in your view? Could anything faulty on the control board produce that sequence of events?

How many relays are involved in the NTC/element control circuit? If there is a relay fed by the NTC itself I could believe that would be at fault if it’s on the control board. However, the power stage relay to the element clearly works, unless there is another power control before it that switches both the element AND the NTC?

Kind Regards,

Joseph

[electrofix]

relay sounds like its ok

you could change the stat

new part no 165281 £24.37 from Bosch

or used

https://www.ebay.co.uk/itm/Dishwasher-BOSCH-SGS46E22GB-82-THERMOSTAT/233786181713?hash=item366ebe0851{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d}3Ag{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d}3AZ1MAAOSwrNBftQIp&LH_ItemCondition=3000

you could try removing plugs from timer and replacing them in case its a bad connection

Dave

Dave

[Author]

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