Water System Woes

As the Club’s Technical Officer I seem to spend quite a bit of time time helping members to sort water system problems.

Touring caravans are fitted with one of two types of system namely micro-switched or pressure switched. The function of the switch in each case is to operate the pump when water is required and to stop it when not.

Each system has its own potential set of problems so we’ll look at each one in turn and then look at general problems that can affect both systems.

Micro-switched Systems
In a micro-switched system each tap contains a tiny switch. When you turn the tap on the switch is operated and the water pumps runs. Turn the tap off and the switch is turned off stopping the pump. Simple. What could possibly go wrong? Well, usually not too much, but occasionally things can go awry.

Switches can go faulty and simply refuse to work or in some cases taps can leak water internally onto the switches causing them to malfunction. Also a tap that is not turned fully off may not be releasing any water but the microswitch itself may not be off and so the pump keeps running. If undetected this can lead to a flat battery and possibly a burnt out pump.

Other problems affecting micro-switched systems include faulty wiring and old taps that refuse to pass water even though they’re turned on and the pump is running. If you’re having problems with old taps the best thing to do is to replace them. This is normally a straightforward job although with some washrooms the whole vanity unit has to be removed to gain access to the pipework.

If you have a tap that will not operate the pump try turning another tap on slightly. With luck this second tap will switch the pump on and allow water to come out of the first tap. This should get you by until you can sort a proper fix.

Pressure switched systems
A pressure switched system is inherently even simpler than a micro-switched one because it contains only one switch and the taps can be of the conventional domestic type. Water in the system is kept under pressure by being trapped between the taps and a one-way valve at the inlet. When a tap is turned on, the water pressure drops. This operates the pressure switch and turns the pump on. When the tap is turned off the pump continues to run until sufficient pressure has developed to trip the pressure switch.

The critical aspect of pressure switched systems is getting the pressure switch adjusted correctly. If it is set too low the pump will never switch on, and if too high, it will never switch off. The other factor in all of this is the pressure delivered by the pump itself. This depends very much on the voltage at its terminals. With the caravan’s mains charger switched on then the 12 volt system could be running as high as 13.8 volts. Switch it off and use the caravan for a day or two and the 12volt system will be down at 12.4 volts or even less.

These two voltages produce significantly different pump performances when associated with the typical type of submersible pump supplied with most touring caravans. A pressure switch set up with the charger switched on may need to be readjusted once the charger is off.
So how do you set up a pressure switch? Well first of all you need to find it. On Whale systems the switch is located at the back of the water inlet and you will see a plastic adjusting screw and lock nut. If you have an on board tank in use then the switch is normally sited on the pipework near to the tank. This often means it can be found inside a bed box. The switch is characterised by having an adjusting knob on top and two wires connected to the bottom.

To adjust the switch turn on a cold tap and close it slowly until the water comes out at a slow trickle. Then adjust the pressure switch until it can be heard constantly switching on and off.

Basically it’s as simple as that but you may need to repeat the exercise if the battery voltage drops.

If you have a motorhome then it is likely you will have an onboard diaphragm pump. The pressure produced by these pumps is much less dependent on battery voltage so you should have fewer problems.

Sometimes no matter what you do it is impossible to get a pressure switched system to work reliably. If this happens try changing the pressure switch. After I did so on my 1994 Corniche the water system worked perfectly for the remaining 5 years I owned the van.

One problem I have seen from time to time with older pressure switched systems is that taps can some times turn themselves on slightly even after they have been properly turned off. The answer is to tighten the gland nut at the bottom of the tap spindle. This causes the spindle to be gripped tighter and prevents it from undoing on its own. If you’re not sure how to do this then ask your dealer to do it or see me on a rally. Not all taps have a gland nut so in these cases replacement may be the only cure.

Problems common to both systems

Sputtering
This is a sure sign of air in the system. Obviously a newly primed system will take a little while to purge its air but if the problem continues beyond that then something is wrong.

On caravans without an onboard tank the most likely cause is a problem with the non-return valve on the water inlet. These valves are simply small rubber ‘mushrooms’ that allow water to pass through from underneath but not back. In use debris can become lodged underneath preventing the ‘mushroom’ from sealing, or the mushroom head can become distorted preventing a seal.

On caravans with an onboard tank it all depends whether the system is pressure switched or micro switched. On the former the non return valve is contained within the pressure switch housing and is generally quite reliable although occasionally a foreign particle may prevent it seating. If there is such a problem not only will there be sputtering but the system will not work properly as it will not be able to sustain enough pressure to keep the pressure switch turned off.

Caravans fitted with an onboard tank and a micro switched system do not usually have a non-return valve in the line back to the tank as it is not strictly necessary. Under certain conditions however some water can drain back into the tank leading to air in the pipes. This can cause sputtering, especially on the hot water side where any air is expanded by heating.

Restricted or uneven spray pattern
This is most often seen on washroom taps where a rose containing many small holes is fitted. The problem is debris building up behind the rose and blocking the holes. On Whale Elite taps the rose can be carefully unscrewed for cleaning. The latest Reich taps have a removable section at the end of the spout. It simply pulls off.

Water leaks at the pump inlet
Firstly it is important to ensure that the connector block is fully pushed home. Assuming this is so then the most likely cause of a leak is failure of one or both of the ‘O’ rings on the inlet housing. However one case I came across was due to the pump connector block being scored on the inside such that the ‘O’ rings could not seal. When replacing these seals it is important to use the correct replacements. I have seen cases where thicker ‘O’ rings were fitted, making the pump connector block very difficult to fit and remove. Do not be tempted to grease the ‘O’ rings to make them easier to fit. Petroleum based greases will be absorbed by the rubber causing it to swell. Silicone greases are much better in this respect but must be used very sparingly.

Water leaks from the flue plate (Carver Heaters)

There are four possible causes. The most common is that the air bleed quick drain screw to be found in the top left hand corner (later heaters only) is open or not seated properly. It has a spring behind it because it also acts as a pressure relief valve. Simply turn it either way until it seats.

The second is that the pressure relief housing is cracked. There are two types of Pressure Relief Valves, the old type don't have the quick drain facility, the new quick release valve can be fitted to the older type of heater but the flue cover will have to be replaced too. If the pressure relief valve assembly is cracked it will have to be replaced. This can be a tricky job. The nut part of the valve isn't easy to get to with a spanner. (You'll need a 20mm one). A socket can be used but the valve is very close to the side of the heater housing so you can put pressure on the threads and the valve may snap leaving part of itself in the flue plate. If this happens, make two cuts about 3mm apart in this remaining part.

Be extremely careful not to damage the cast threads of the flue plate. Next use a small screwdriver underneath to remove it. It should then be possible to collapse the remaining part of plastic inwards and remove it.

The third is that the 'O' ring that seals the drain plug is defective. This is usually easy to spot and remedy.

The fourth possible cause is that the water tank has been ruptured through frost damage.

No flow from the hot taps
This problem can occasionally occur on Carver water heaters when priming the system for the first time after being drained down for the winter. The is cause down to the non-return valve on the cold water inlet to the heater, which can become displaced by ice or reverse pressure such that it will not allow water in. It is sometimes possible to fix this fault without replacing the valve although replacement is usually the best option. Removal is simply a matter of removing the cold feed pipe and unscrewing the valve fitting to which it was attached. One of our members was wrongly told he needed a new heater when this happened to him!

Water not heating on electricity
Three easily rectified problems can cause this to happen. The first is that the plug carrying the mains supply to the heater has become disconnected or faulty. The type of plug will depend on the age and type of heater. Some look very like an electric kettle plug. Later heaters are fitted with JST type plugs and sockets, which are not dissimilar to those sometimes found on car wiring. With these plugs it is possible for one or more pins not to be fully latched in place during manufacture.

The second possibility is that the high temperature cut-out has operated. Look for a red button on the end of Carver heaters. On later heaters this button is hidden behind a hinged cover.

Lastly make sure that none of the isolating switches on the electrical control panel has tripped. If a switch will not reset, call in a qualified electrician.

Water not heating on gas

A good12 volt supply is necessary to operate both Carver and Truma heaters on gas so this is the first thing to check. Secondly make sure that the isolating valve on the gas distribution manifold has not been accidentally closed. These manifolds are often situated in the bottom of kitchen cupboards and the water heater tap is usually coloured red.

Older Carver heaters have a small beige coloured control box nearby. This contains two small glass fuses that can fail after a number of years. If you are lucky there will be two spares inside the box itself.

If none of these is to blame then the fault may lie within the heater itself.

Truma Ultrastore Water Heater

I have come across a number of cases of Truma Ultrastore water heaters lighting but not staying alight for more than about a minute, especially in breezy conditions. The problem here appears to lie within the electronic control unit inside the heater. I suspect the flame sensor is not adequately sensing the flame. Thinking the flame has gone out it therefore switches the heater off to prevent a build up of unburned gas. If this problem happens to you you’ll need to ask your dealer to investigate.