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The machine is a Hotpoint 7801P slimline dishwasher built 1992.
After a month or so of lack lustre performance one day it refused to heat. On closer inspection the spray bars do not seem to be getting much flow/pressure. When the door is opened smartly during the wash cycle the lower bar is just moving with some water limping out and the top bar is still, with no evidence of water reaching it.
I checked the level-pressure switch which appears to be a single level (simple dishwasher) changeover type with three contacts (marked 1,2,3). The pipe feeding the switch is clear and can be easily blown through into the sump. The switch operates (clicks) when blown by mouth and 1&2 break. However when 2&3 make, a slight bit more pressure opens them again. Its difficult by mouth to get just the right amount of “blow” to keep 2&3 on. Contacts 1&2 remain cleanly broken after the click, until the pressure is released.
So it looks like the switch is knackered with this weird behaviour. Firstly any thoughts on this ?
Secondly can this fault explain why the symptoms of no heat and possible low circulation flow (I may not have opened the door fast enough 😕 ) occur ?
I’m reluctant to replace this £40 item on spec on this old machine unless it appears to be the likely culprit.
thanks for any help.
Re: Hotpoint slimline DW doesn’t heat
Sapus
Please remember to switch off and remove the plug before attempting anything on the machine.
The pressure switch contact notation is 1-2 NC 1-3 NO so 2 and 3 should not come in to the equation.
The water inlet is via a metering tank and your poor fill is probably due to a blockage somewhere in this tank or associated hoses.
The heater does have a protection switch which does not allow heat if there is insufficient water in the machine.
If you feel you need a professional then go to the repairs@ page for your nearest engineer.George
Re: Hotpoint slimline DW doesn’t heat
On these machines if there aint enough water in machine the flow through the heater the heater wont activate the press sw on the top of the heater resulting in no heat, could just a simple blockage causing it.
Re: Hotpoint slimline DW doesn’t heat
Thanks for these thoughts guys.
My first thoughts were also a blockage of some sort just because of the low flow, and this in turn stopping the heater. I was checking out the pressure switch on advice from a professional repairer I know (180 miles away unfortunately).
btw George you are correct, I didn’t notice the terminals were not numbered in logical order. The middle one is the pole of course. 1-2 is NC and breaks OK 1-3 makes momentarily as I said. On at 50mm off at 51mm water. But I believe this maybe intentional because the on band seems to be adjustable. Not sure how this would function in the machine? See the switch at http://www.bitron.it/products/eldom/pdf/press-760-e.pdf
I notice you can see nicely into the metering tank. Any idea how the flow is supposed to make its way through the maze ?
You were quite right also George with the advice about removing the plug before charging about inside any electical gear, especially with water about. As a Chartered Electrical Engineer I know this only too well, but unfortunately little about the inards of the average dishwasher.
Once again any more details or theories would be much appreciated.
Re: Hotpoint slimline DW doesn’t heat
The solution to this problem is very simple – percussive maintenance. At the bottom of the fill matrix is a large brown resin chamber. Over the years, this slowly solidifies and the water can’t run through it any more. Given that the fill is a metered dose from the fill tank on the back of the machine, it has about 3 minutes to fill – this leads to underfilling and insufficient water being circulated to operate the pressure switch on the heater.
So what you do is – beat the chamber. Gently, persistently with a soft handled screwdriver handle. Possibly for a long time. When the gel starts to behave like a sand picture, you’ve solved it.
Sounds mad, but it works. Don’t tap too hard, or you’ll crack the chamber.
Good luck,
Penguin45.Re: Hotpoint slimline DW doesn’t heat
Penguin45 is of course talking about the water softener resin chamber, which may have solidified alright, the time taken depends on the water hardness. Your machine may have passed the point of no return but just incase, the magnesium and calcium salts which cause this can be easily removed by adding dishwasher salt to the machine. Regularly in hard water areas and less frequently in softer. Even in very soft areas the chamber needs a flush through maybe every six months to get rid of accumulated hardness. How hard is my water? check your kettle element or look on the side of a packet of Ariel for a rough guide to the UK.
George
Re: Hotpoint slimline DW doesn’t heat
I’ve given the resin matrix a good beating with a rubber mallet and its certianly nice and free now. When filling all the resin grains swirl around with no clogging of any kind, and look nice and clean. However I’m not convinced it was solid in the first place since I didn’t pay it much attention before beating it. As regards salt, the machine has never been used when the low indicator is visible. We’ve been quite religious about this, even though its not particularly hard round here.
I cannot see a fill tank on the back of the machine (behind the cabinet) only the matrix on the left. I would think if it needs one it must be incorporated into the matrix. I’ve noticed the fill passes through the resin up a column to the rear and then I loose track. The larger chambers to the rear and above the salt chamber always remain full at any time, and the salt chamber is mostly empty with only about 4cm of water in it with no apparent activity or flow here at all. Does that sound right ?
Anyway after all that beating nothing has changed, and it remains precisely as it started 🙁
I noticed on the Prewash programme it fills twice and drains without doing any circulating. It then fills a third time and begins immediate circulation. Not sure what the point of the 1st two cycles is.
Anyway still no decent flow to spray bars or any heat ??
I suppose I will need to start stripping it down further to look for a blockage. Not sure how to get the tray off the bottom. Looks like the machine has to go on its back, to allow the tray to hinge down ?
Any further pointers guys ?
Re: Hotpoint slimline DW doesn’t heat
On the 7801 the prefill tank on the rear was ommited, this feature enabled condenser drying, but on this one they reverted to the normal heat/ time lapse drying cycle. The water in chambers that remain full is used for filling up the salt and then through the resin on regeneration. depending on the setting of the regen switch (top left front) 1,2, or all 3 empty. Regeneration valve opens just before the drying cycle at he end of the rinse period. That’s probably all we can help without seeing the machine, by the way you are correct in that it’s laid on its back to drop the base.
George
Re: Hotpoint slimline DW doesn’t heat
sapus wrote:
I’m reluctant to replace this £40 item on spec
Current list price for a 1800026 pressure switch is around £21.00 + vat.You could try and measure the amount of water going into the machine, by filling on a Prewash then collecting the water discharged after the third fill and circulation ( I cannot see the point of two drain/fill sequences on Prewash either but that is correct according to the sequence chart ), you should get around 4.2 litres of water. If you do then the machine is taking in the correct amount of water, that would suggest an internal blockage is causing poor circulation resulting in the heater protection switch isolating the element. It could be a circulation pump impellor failure but I have never seen that on this model. Are all the holes in the spray arms clear?
Re: Hotpoint slimline DW doesn’t heat
Well, I removed the bottom tray, the circulation pump and the heater unit.
All very clean no sign of blockage or even scale on the heater element. Heater measures reasonnable 20 ohms (about 3kW). Flow switch operates fine and the thermal (I presume) cut-out on the side of the heater was on as expected.
Pump impellor looked OK, all blades present, and spins smoothly. The pump did however have slight plasticy rattle when shaken, and the back of the impellor blades had perhaps 2mm clearance (from memory).
Put it all back together and of course there was no change since I’d done nothing. I then checked the amount of water taken in, and thanks for that useful information “iadom”. It was 3 litres exactly. So I adjusted the pressure switch and brought it up to the required 4.2 Made no difference still low flow, cannot make it up to top spray bar.
(btw I was quoted between £33 and £60 by 5 or 6 internet based suppliers for the Press switch + carriage)
Checked spray bars, and all clear.
So I suppose it must be that pump impellor clearance; the pump appears to spin round nicely when powered up ? So looks like thats the end; I doubt a pump is peanuts.
Spare parts for a 7801 anyone ? got a good heater, and various switches etc ….
thanks everyone for the assistance
What does anyone think of Beko ?
Re: Hotpoint slimline DW doesn’t heat
Beko are made in Turkey and are not a premium product, spend a little more on a Bosch with 2 years full parts & labour warranty.
Circulation pump for a 7801 is just over £62.00 + vat. To be honest, one or two minor parts are already listed as obsolete for your machine so it may well be time to move on.
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