How the water system works - pumps and microswitches.

I have seen a lot of questions recently about the water system in Classic Hymers.

Here is a rough description of how it all works - remember we are usually talking pre 95 vans, and different vans have different layouts. Also remember that in any old van, previous owners may have made modifications.

There are 4 main components to the basic water system - the fresh tank, the pump, the pipes and the taps. 

The original system is what is called a switched pump system. This differs from a house system in that it is not pressurised. In a house, the mains water is under pressure, so all you have to do is open a valve (a tap) and out comes the water.

In a switched system in a Hymer, there is a 12v pump submerged in the water tank. The pump is attached to a pipe that leads to all the taps. Each of the taps has a switch in it, and these switches are connected to the 12v battery system in the van. Every time you open a tap, not only does a valve open, allowing the water through, but the switch closes and supplies 12v to the pump so that the water flows. When you close the tap, the pump stops.

The reason they do this in motorhomes is that it is less risky to the van if there is ever a leak. If a pipe bursts, or leaks, or there is a loose connection in any of the pipes, the leak is limited to the amount of water in the pipes, and the whole tank will not empty into the van. This helps to prevent catastrophic leaks that can lead to expensive rotten damp damage. Of course it is not totally foolproof - if there is a slight leak that only drips a few drops every time a tap is operated, this can also lead to damp and rot damage. So in an old van, ot pays to regularly inspect your water system.

The switches inside the taps are usually called microswitches. If you look at the underside of a tap, you will see the water pipes going to it, and also 2 wires. In  some taps, these microswitches can be replaced - see picture below for a typical example.

If you do not hear the pump operate when you open a tap, and no water flows, then that is usually a sign that the microswitch isn't functioning. This can either be the switch itself which needs replacing, or the wires to the switch have come loose or damaged.

Another reason is that the pump is broken, or the wiring to it is broken or corroded. See troubleshooting common faults below ...

An idiosyncrasy of the system is that any tap will operate the pump, so if you have a broken switch in one tap, you can still get water out of it by opening any other tap. For example, if your shower tap isn't working, just opening another tap slightly, just enough to make the pump run, will enable the water to flow from the shower.

The next component after the pump is the manifold. A single pipe runs from the pump in the tank to a distribution manifold. This looks like a tube that has several pipes coming from it - see picture. It enables a single pipe to be split into several more pipes. In a normal setup, there are 2 manifolds, cold and hot. The cold feed from the tank goes to the cold manifold, and from there there is a cold pipe to each tap - usually kitchen, bathroom and shower. In some vans the bathroom tap and shower is a combined unit. From the cold manifold there is also a feed to the Truma hot water boiler, and then the hot water from the boiler goes to the hot distribution manifold, and from there hot pipes go to the taps.

On some older vans there are no manifolds - there are just a succession of T joints, which achieves the same thing - distribution. So if you don't find a manifold in a pre 1990 (roughly) van, look for T connections.
 
There are usually also 2 drain valves, one in the cold side and one in the hot side - both usually adjacent, and connected to, their respective manifolds. The cold drain valve usually has a metal body and a red or yellow plastic handle. This is to drain down the entire system for winter storage. The hot drain valve is grey plastic and looks quite different - to open it you unscrew the top. This will drain down the hot side of the system and is useful when you just want to work on the boiler, for example.

To drain down a van for winter, drain the main tank, isolate the pump - usually by switching off all 12v to the van with the big red isolation switch - open all the taps, and open the main drain valve. All the water in the tank and system should then drain onto the floor and the pipes should all be empty, and not prone to frost damage. Some main water tanks have drain plugs, which makes draining quicker and easier.

Then leave all the taps open and the drain valve open for the winter. Don't forget to close it before you fill up in spring, and it is always a good idea to check every joint for leaks and drops at the beginning of a new season.


Post 95 vans often have 12v electrically operated valves with thermostatic control - they will automatically open in a frost. After 25 years these get unreliable and are often replaced with manual valves, or held closed with wire or cable ties. But pre 95 classics have manual valves.

Taps - Usually in Hymers and most motorhomes, the taps are mixer taps, rather than individual hot and cold. A mixer tap has both hot and cold pipes leading to it. There are many types of taps - too many to list individually. Some taps have red and blue plastic push fittings, others have normal spigots and jubilee clips.

Common faults

As already mentioned, the commonest fault is a faulty microswitch. You may be able to replace the switch. Sometimes owners take the opportunity to replace an old tap with a new modern one. The modern silver Reich single level mixer taps are a common choice.

There are too many different taps for specific instructions, but here are a few guide notes. Look for "tails" many taps have factory fitted pipe tails, and it is the tails that connect to your pipes. Other taps have push fittings - so if you see no jubilee clips or other fixings, and wonder how on earth the pipes are connected, then get a grip and pull. Google for "caravan taps" and you will see lots of pictures. Most taps are secured to the sink by a large plastic nut. You may think - how on earth do I get a spanner on that - usually, you don't have to - it will be only finger tight. It may be stiff with age, but do your best to exert maximum force with your fingers before giving up!

If your switches are OK, and the pump is not running, then the pump, or the wiring to it, is suspect. The thing to remember about the original submersible pump, is that they are not intended to last for the life of the van - in effect they are a consumable. They rarely last more than 10 years in regular use, and they often can, and do, fail, especially after a long period of storage. But they are cheap - every caravan shop sells them, and any 12v submersible pump will do, from a cheap single barrel Whale, up to a Reich double barrel costing over £60 ... Most owners carry a spare, but they are easily available in all countries.

But before you buy a new pump, here are some tips to revive an old pump. They work very simply - a small 12v motor turns an impeller. Similar to a fish tank pump. The impeller can get stuck. if you have easy access to your tank, and can get your hand inside, reach into the water, grab the pump (with power applied by an open tap) and give it a good shake and knock - this will often free the impeller. If this doesn't work you can take the pump out and try again in the dry =- you may find the input chamber is gunked up.

The next commonest fault is a leaking manifold. The original plastic Hymer manifolds are subject to a lot of vibration over 25 years of travelling, and eventually they are known to develop cracks. Many a rotten floor has been caused by a leaking manifold, so it pays to inspect your manifolds regularly. If you do find a leak, you have several options. You can buy a new manifold from Hymer or any spares supplier. The new manifolds are stronger, but they are not cheap. Many owners make their own manifolds. There are several ways to do this - all you need is a method to join 4 or 5 pipes together. Popular choices are compression "T" fittings, or copper fittings. See pictures. As long as it is strong and watertight, you can use whatever method suits you.

Manifolds can also suffer from calcium deposits that build up over many years which can result in reduced flow. This is dependent on the hardness of the water regularly used to fill the tank. if you live in a hard water area and regularly have to descale your kettle, and you regularly fill up the van with the same water, this can happen. manifolds can also get clogged up with other debris.

The way to check if a manifold is in good condition is to identify the main feed to it. Then clamp of the pipe and undo it from the manifold. Then, with the pump running, release the clamp and let the water flow into a bowl or old towel. if the flow is strong, but the flow coming from the taps was weak, then the manifold is suspect. But if the flow is weak, then the pump is suspect.

Also, usually close by the manifolds, or close to the Truma boiler, you will find a drain tap. This usually leads from one of the manifolds and is a tap valve mounted on the floor. It has a lever on it to open or close it. This is the drain valve, and is used to drain down the system for winter storage. Draining for winter storage minimises the potential for frost damage to the pipes.

The waste water system - also called grey water.

Water that goes down the plug holes flows through grey waste pipes. These are slightly bigger than the water feed pipes, and they are different in that they are rigid pipes, joined together with push fit elbow joints. They usually are arranged in 90 degree angles. Under each plug hole is usually a trap - same concept as a domestic U bend, but these are usually round traps with concentric circular chambers that fulfil the function as a U bend, only in a more compact format. these are usually made by Reich. These traps are susceptible to clogging with old age - they get full of grease and gunk and old hair. 

These traps are serviceable. They can be removed by pulling off the grey waste pipe and then undoing the central screw in the  plug hole. They have a circular cover on the underside that can unscrewed revealing the insides. WARNING! Removing and servicing a trap can be fraught with difficulties and gotchas. They can get very stiff with old age - removing them can break or crack the hole in the sink. Very often when you screw back the cover of the trap, and the trap itself, you don't get a good seal and you will get a leak. It can be an extremely frustrating job, so my advice to you is not to take it on unless there is no alternative.

If you have a blocked or slow trap, try everything first before removal. If you do remove, be ready to order a new trap - it might be the only solution, so remember this if you are on holiday. Try boiling water, chemicals or gentle plunging. Trap removal should be a last resort, and only then if you have the skills, time and spares to deal with the job going wrong.

From the trap, the plastic waste pipes lead to the waste tank. As already mentioned, these are straight lengths of plastic waste  pipes joined with 28mm compression elbows. These elbows are prone to splitting and leaking, and again, benefit from regular inspection. There are no junctions in the waste pipes - they lead individually from the sinks/showers directly to the waste tank, where they enter into the top of the tank through elbows and big rubber grommets. The place where they do this is usually accessible, usually underneath a wooden panel. Another common fault is that many years of vibration can work the joints loose, resulting in leaks. They can also split with vibration and old age. Split elbows can be repaired using modern sealers and plastic glues. If using sealer to repair, the mating surfaces must be super clean. 

But please don't panic thinking that the system is unreliable - leaks are quite rare. All you have to do is to use common sense. 

Maintenance

Just as you maintain the rest of your van, it pays to maintain and check your water system, because leaks can cause expensive rot repair bills. All you have to do is keep an eye on things. 

Taps - every few months, put your hand up under the tap where the pipes attach, and feel for water. Same for the traps and waste pipes - obviously you can't get at all of them, especially the shower trap, but know your van, and take a regular look.

Everybody cleans out their boot or storage area occasionally - when you do, check for wet patches. Also - know where your manifolds are, and check regularly for leaks.

Another tip is to wait until somebody is having a long shower and look under the van for any tell tale drips, especially in the area of the shower tray and the grey tank. Do this once or twice a year.

Pump. Carry a spare!

Winter storage - draining the system.

Pressure Systems

Some owners decide they want more pressure than a submersible pump can provide. So they convert their water system to a pressure system. This is similar to the system used in yachts and boats. In a pressure system the submersible pump is discarded, and replaced by a simple pick up in the tank. The pump is then mounted externally to the tank. Popular pressure pumps are made by Shurflo and Whale. A pressure pump switches on when the pressure drops - ie a tap is opened, and switches off when the pressure increases - ie a tap is closed. This means that the entire system is permanently pressurised, just like in a house.

Advantages. Higher pressure - much higher than a submersible pump. Better showers.

Disadvantages. More prone to leaks, and when leaks do occur, they can be serious. Because the original van pipe system was designed for a low pressure system, and in the case of an old van - is old ... then suddenly increasing the pressure can result in new leaks occurring. So in the days and weeks after upgrading to a pressure system, all joints, taps and manifolds must be inspected and tightened if necessary and checked for leaks. This is not to say that the pipe and tap system is not suitable for higher pressure - it is, but it needs to be checked in an old van.

The other problem is that if a leak does occur in a pressure system, the pressure will drop, and the pump will operate - usually in small pulses. If the van is unattended, then the entire tank can be emptied through the leak, which isn't good. For this reason, pressure systems should have an isolation switch which cuts power to the pump, and the pump should be switched off when the van in unattended.

However, the upside of this, is that of you do develop a small undetected leak, the pump will pulse occasionally as the pressure drops, giving you warning. The pump will occasionally pulse randomly, but if it pulses regularly, say every 15, 30 or 60 minutes or so, then that is a sure sign of a dripping tap, or a leak.

Another thing to consider with a pressure system is that you will use more water. This can be an issue with showering, as too big a flow rate may empty your 10L hot water tank before you have finished your shower ... so there is a balance to be made.

Finally a few random notes. If you get black stuff in your mixer taps - this is a harmless bacteria. You can treat it with Elsil. 

Owners often ask if they should drink the tap/tank water. Other than making sure that the water is fresh - ie not from last summer! Then my answer is yes. There is no reason for your water system to be any worse than the mains pipes that deliver to your house. You may detect a plastic tinge from the tank. But basically it's up to you. I use it for tea and coffee, but for drinking water we refill containers with tap water. However, if necessary, I have no problem drinking it, and have done so for 20 years in many countries. You can buy filter systems, but I have no experience of these.

Manifolds - top one (hot) is a Hymer original. Bottom one (cold) is a home made copper one. You can also see the hot system valve at the top of this manifold.

Another example of alternative, stronger manifolds - these made by Snailvans in Leicester I believe.

Drain valve - also available in red!

A new Reimo manifold - not cheap!

Typical Microswitch

Typical modern mixer tap - many other designs available

A typical external 12v pressure pump

A typical standard submersible pump

Typical tank layout
The pump is submerged under the orange hatch. Black hatch is for inspection/cleaning - it can be other colours.

A= Main feed pipe to water system (taps etc) with non return valve to stop system siphoning back

B= Tank venting to allow filling without blow back at filling point 

C= Non return valve allowing air back into the pump allowing it to drain and be frost protected when the tank has been drained. 

Typical concentric odour and waste trap - one end is usually blocked off, and in Hymers they are usually white. 

Waste pipe elbow - occasionally prone to splitting with old age.