Last modified on 16 June 2009, at 20:56

Do-It-Yourself/Fixing a dishwasher

THE DISH WASHERS NOT WORKING PROPERLY - WHO’S TO BLAME?

Three items need to be considered when a problem arises with a dish or glass washer that doesn’t perform properly. The items are usually maintained by three different companies. Each of these companies usually specialise in a particular area.

An under performing dish or glass washer could have a major effect on a business. If the crockery and table ware are not cleaned and sanitized correctly, customer satisfaction cannot be guaranteed. Unclean crockery can also pose a potential health and safety risk. Three companies may need to be contacted to resolve a simple issue. Those company’s usually have little knowledge of how another company’s equipment or products work. It’s the dishwasher company that initially gets the call to fix a problem dishwasher. When the matter cannot be resolved they will often blame another company’s equipment or product. Does this sound familiar! With minimal knowledge a poor performing dishwasher can be made to work effectively. After all, all that is required is for the dishwasher to clean, sanitize and dry the crockery in the shortest period of time.

The items that usually have an effect on the overall performance are;

Water Quality –The dishwasher must have a softened water supply. Chemical – Good quality chemicals dosed at the correct rates are required. Temperature – The wash tank and rinse boiler must be at the correct temperature.

Another factor can be poor machine selection when purchasing new equipment.

What’s right the right machine? The cheapest product will not give the best results and service. When buying a new dish or glass washer, the decision is often price driven, this is a major mistake. A number of dishwasher distributors will not have the knowledge and understanding to help the buyer make the right decision. This can turn out to be a costly mistake and will often come back to haunt them in later years. It is always worth asking the manufacture for help and advice before making that final decision. Many of the bigger brands will appear to be more expensive, but in the long run they will work out cheaper as the manufacture can offer a longer after sales service. Winterhalter, Hobart and Meiko are renowned for their after sales service.

The dishwasher supplier should be asking specific questions before he attempts to sell a dishwasher. He needs to know what the dishwasher will be used for. Is it for ceramics? Is it for glassware? Is it for both? Do you have a softened water supply? How busy is your business? The dishwasher must be able to cope with the busiest times. All manufactures will quote a “Plates per hour” rate. This will vary from manufacture to manufacturer and is determined by the basket size / cycle speed. The cycle speed is usually determined by the recovery rate of the rinse boiler. The branded machines will usually have the shorter wash cycles and the higher plates per hour rates.




There are four basic types of dishwasher. 1) Front loading - Cabinet type (small) – Mainly used for washing glassware in the bar area or used by very small businesses that have minimal space available.

     Cabinet Type (large) – Used by small to medium sized businesses to wash  
     glassware and ceramics in the bar or kitchen area.

2) Pass Thru - Used by medium to large businesses. The pass thru machines can wash high volumes of product. These machines can have an external flexible pre wash system fitted. 3) Flight / Rack Machines – This type of fryer is used mainly in the large businesses like motorway service areas, airports, hospitals and large schools. There are two types of flight machine. One uses baskets that are either pushed or pulled through the dishwasher by a mechanism and the other uses a continuous conveyor system. The rack system is more efficient to use 4) Utensil Washer – Mainly used by the larger businesses for washing large pots and pans. It’s only the large branded manufactures that can supply this type of item.

A business ideally needs two washers, one for ceramics and one for glassware. The reason for this is that ceramics and glassware are manufactured in a totally different way. The ceramics are specially vitrified for the hospitality market to make them very durable. The glassware cannot be vitrified. Most chemical companies market two products, one for ceramics and one for glassware. The glass wash chemical will contain less caustic and should not cause any damage to the glassware. Dishwasher suppliers are not always aware of this fact. The reason why many of the bigger businesses have two dishwashers is, is that the dishwasher used for cleaning ceramics will be washing greasy items. If glassware is washed in the same machine the glassware with become smeary.

Most small to medium business do not have the luxury of space and can only have one dishwasher. The chemical that is usually purchased for this type of operation is usually the product designed for ceramics.

The dishwasher supplier should be able to give help and advice on the best type of machine for any business. It may be worth getting the manufacture involved at an early stage. This should ensure that the best advice is given from the on set.

TEMPERATURES

Wash tank and rinse boiler temperatures are usually the cause of poor performance. If the wash tank temperature is not correct at the start of the washing session, the dishwasher will struggle to wash the crockery properly.

New equipment will come factory set and should therefore require no adjustment. If a problem arises with performance the temperatures must be checked as part of the elimination process.

The adjustment of the temperatures settings is usually the quick fix solution to most performance related issues.

The temperatures that are crucial are the wash tank and rinse boiler temperatures. At start up the wash tank temperature should be at least 60 - 65 degrees, but not less than 60°. The wash tank temperature can be checked by the operator using a temperature probe. If the temperature is less than 60 degrees the final wash will probably be poor. If the temperature is below 60 degrees the wash tank temperature will need to be adjusted. An extra 5 degrees in temperature will make a significant difference. Lack of adjustment can be an indication that the heating element may have a fault or is breaking down.

Care must be taken with cabinet style machines. If the wash tank temperature is to hot the door could blow open on start up. This could also be an indication that the door catches are worn.

The rinse boiler should achieve a temperature of 85 – 90 degrees before the end of the wash cycle. This is the optimum temperature required to ensure the crockery dries effectively.

The checking of the rinse boiler temperature is more complicated and should only be carried out by a competent engineer as is located within the body of the dishwasher. The engineer will require a thin probe or temperature sticker to carry out the task. If the rinse boiler struggles to get to temperature it may be scaled up. Evidence of scale in the wash tank will mean that the rinse boiler has scale in it to. If the scale build up is too severe the only options available are to replace the machine or have it repaired. Rinse boiler and rinse boiler elements repairs are very expensive. Evidence has shown that when a water softener is fitted to a dishwasher the life of the dishwasher is increased. Softened water will assist with the overall wash quality.

Note The wash tank and rinse boiler temperatures must only be adjusted by an experienced and qualified engineer.

The average janitorial suppliers are not aware that the machines temperatures can have a major effect on the overall performance.

A number of the larger branded chemical suppliers in the industry train their sale forces on dish washers and dosing systems and can offer advice.

The average engineer that comes to look at a problem machine may have little knowledge about chemical dosing systems, chemicals and water softeners.

WATER QUALITY – WATER SOFTENERS

Dishwashers must have “break tanks” or a suitable facility fitted to stop the flow of water going back into the water supply system. This is a legal requirement and is enforced by the water authorities.

There are various types of water softener and they all have varying rates of capacity. The capacity is the amount of softened water that it can deliver between regenerations. Regenerations are carried out manually or automatically to renew the water softeners efficiency. The regenerations must be carried out at scheduled intervals, without fail!

All dish washers should have a suitable water softener fitted. Water softeners will eliminate scale if used correctly and will help to protect the initial investment in the equipment. The softeners capacity must be large enough to cover the busiest periods.

Manual regeneration The customer has to physically carry out the regeneration process. These are generally the “stainless steel tube” type often associated with the pub trade. They are simple in design, easy to use and are fairly cheap to buy and are readily available from Companies like First Choice Catering Spares of Cannock.

Cartridge type The service company installs a cartridge system that removes the scale. The cartridge has to be renewed on a regular basis and can work out to be expensive in the long run. These are usually attached to low volume glass washers where space is limited.

Automatic Regeneration These come in various shapes and sizes depending on the application. They are similar to the units that would be used in domestic houses. There are three types.

1) This regenerates its self at a pre determined time on a day or day’s pre set by the user. Depending on how busy the business is will determine how often if it will need regenerating. 2) This is a totally automated system. It will calculate the through put of water and regenerate when the water softeners capacity has been used up. 3) This type of system has two or more water softeners in situ. These are used for high water consumption businesses. The system automatically switches from one unit to the other to give a constant supply of softened water.

Important note All water softeners have a maximum capacity. This is often overlooked.

On many occasions someone forgets to calculate the actually volume of soften water required. In many instances the soften water required during a service outstrips the capacity that the water softener is capable of producing between regenerations. In many cases all the capacity will be used up in one service. During the second service the glasses will appear dull or the plates will become slightly rough to touch. This is because no softened water going through the machine. The same old cycle happens day after day, but no one knows why.

All water softeners manufactures should be able to advise what capacity of softened water their product can produce. When this information is made available calculations can be made to ascertain the effectiveness of any water softener. A larger or modified version can then be specified. It’s pointless to supply a water softener that cannot match the consumption required by the dishwasher.

The writer of this article had to modify a standard water softener so that it could regenerate twice a day instead of once a day. A well known dishwasher manufacture miscalculated the water usage after supplying a new water softener to a large school. They had just installed a new 40k flight dishwasher. By modifying the water softener, the softener was able to regenerate twice a day, once at two o’clock in the morning and then at two o’clock in the afternoon. The softened water capacity was exhausted by the time the lunch time service had finished. The modification ensured that the dishwasher received softened water during the busy evening service.

The question often posed is. Why would we need a water softener fitted to the dishwasher when the building has a softened water supply already? The simple answer is, if you get your calculations right you might not need one. Does anybody know what the rest of the building is drawing during the day? The answer is simple, nobody knows. When you have a dedicated water softener attached to the dish washer the maths is so much easier to do.

The calculations are: Based on a reasonably busy site.

Wash tank capacity (40 litres) = initial fill plus 3 litres (water) per cycle x the number of cycles over the daily period.

i.e.: 80 baskets per session x 2 (Lunch & Evening) 3 litres of water per cycle

80 litres (2 initial fills)

480 litres (160 baskets @ 3 litres) Daily water consumption 560 litres

This site would need a water softener that has a capacity to produce at least 700 litres of softened water per day. Note: After regeneration, the water softeners efficiency will start to reduce.

Now you can see why it is so important to know the capacity of the water softener.

Most automatic water softeners have an override facility that can allow an operator to manually trigger the regeneration process. The majority of operators would not know how to carry out this process. They would definitely not know when to do it. There is also much confusion with “When do we put the salt in?” “Do we use tablets or granules?” The key here is to seek advice from the water softener manufacture. The unit will not work without salt.

CHEMICALS There are a large number of dishwasher chemical manufactures in the UK. All will say that their product is better that their competitors. A large percentage of chemical users will buy on price alone. Cheapness will not get you the best results. Most of the major groups will buy good quality branded products from recognised manufactures.

As a rule of thumb, the cheaper the product, the high the water content is. This statement can be justified if a refractometre is used to test the chemical products. The refractometre measures the light (refraction) that passes through a substance. If you measure like for like products the results are instant. The quality products produce a higher reading on the scale. Due to the expense, very few chemical salesmen use a refractometre.

Dishwasher Chemicals When measuring like for like dishwasher chemical “ceramics” an allowance must be made for products that contain a water softener. All dishwasher chemicals will contain a degree of water softening agent, its part of the product make up. The branded manufactures can supply two types of chemical. One has a low and one has a high concentration of water softening agent. If your dishwasher has a water softener and is working well you do not need to buy a chemical that has a high concentration of water softener agent. The chemical with the higher concentration will be more expensive than the product with the lower concentration. They will probably need to be dosed at the same rate. It would be recommended to use the higher concentration product with a machine that has no water softener attached to it. The better option would be to fit a water softener to the machine.

Note: The average buyer will not be aware of the information above. Many will simply buy on price. They just see a like for like product and buy the cheapest...

Glass washer Chemicals Glass wash chemicals are similar to dishwasher chemicals. Care must be observed when buying glass wash chemicals as they have to be milder than dishwasher chemicals. Some of the cheaper manufactures may make one product but market them as two different products, namely, Glass Wash and Dish Wash. If the product is too harsh and dosed at the wrong rate the glassware will become badly soiled and pitted.

Rinse Aid A good quality rinse aid dosed at the correct rate will give excellent drying results. The quality rinse aid solutions are Isopropanol based. The product should look clear and very viscous. The rinse aid is “dosed” pumped or injected into the rinse boiler. If too little product is dosed the crockery items will fail to dry properly. The rinse aid solution will also kill some of the foam that accumulates during the wash cycle.


Dosing systems

1) Manual – The customer manually puts the chemical into the dishwasher. This is not the best method as the process can be very erratic resulting in poor results. There are also the health and safety implication to consider.

2) Timed – Mainly used on the larger cabinet, pass thru machines. This method is very cost effective. Measuring glasses can be used to calculate the exact quantities required. You can work out the cost per basket using this method.

3) Sensored – These are used on the larger flight and pass thru machine. The system works very well as long as they are set up correctly. It has been known that a faulty sensor can make the system pump through a whole container of chemical in a very short period of time. The rule here is to keep the sensor clean. The sensored systems tend to over dose when the machine is initially filled.

Most of the larger chemical companies will supply the dosing units. This ties the user in for a period of time. Always ask the engineer fitting the dosing unit to explain why he has set the system the way he has.

If a problem occurs and the results are poor, the chemical company will simply increase the dosage. They may neglect to check that the temperatures are set correctly. They will probably not check to see if the water softener is functioning properly.

SUMMARY. If you are experiencing problems with any commercial dishwasher you must ensure that all the companies talk to each other. It’s no use one company doing one thing and relying on the other companies to do their thing. A coordinated effort by all the companies will resolve the issue a lot quicker.

Buy the best chemical you budget allows and ensure that the dosing system is working correctly.

An annual service will ensure that the dishwasher functions properly. A few of the major manufacturers offer various service contacts that are very reasonably priced. The service will ensure that the temperatures, dosing systems, wash pump, rinse boiler, wash arms and general items are working properly.

It you have a water softener ask the manufacture if he thinks it is suitable for your type of machine. Often a larger dishwasher is purchased without any consideration being given to the water softener capacity.


Malcolm Morris – 4th November 2005