What is the difference between positive and negative head?

A gravity-fed system is either positive or negative head. In a positive head system a water flow rate of at least 2L/min exists from gravity alone. In negative head systems the water flow rate is less than 2L/min.

When choosing which pump you need it is important to know if the system is positive or negative head as incorrect selection can mean the pump won’t work.

A positive head pump will only work in a positive head system and a negative head (universal) pump will work in both a positive and negative head system, so if you are not sure choose a negative head pump.

Click here to learn how to determine if your system is suitable for a positive head pump.

How can I check whether my system is suitable for a positive head pump?

A positive head pump will activate when a minimum flow of water passes through the pump and out of the pumped outlet, such as a shower or tap, naturally (without assistance from the pump). The minimum flow rate required for our positive head pumps is 2 litres of water per minute (L/min).

You will need to measure the flow rate to determine if a positive head pump is suitable for your system. You will need to test all outlets, such as showers and taps, that are going to be pumped to determine if they have the required minimum flow rate of 2L/min. Watch our video to learn how to measure the water flow rate.

If you cannot measure the water flow rate, then you can check if the system is suitable for a positive head pump if there is more than 600 mm between the base of the cold-water storage tank and the highest point in the system after the pump.

If you are unable to achieve the minimum flow rate of 1 litre per 30 seconds from all outlets that are to be pumped you will need to install a negative (universal) head pump.

What is regenerative shower pump and how does it work?

Regenerative shower pumps, such as our CT range of pumps, have a water wheel impeller inside the end of the pump. Water enters the shower pump through the inlet, the impeller spins the water around inside the impeller casing, building pressure as the water travels around the end of the pump. Between the inlet and the outlet of the shower pump there is a stripping block, this strips the water from the impeller and directs the water out of the top of the pump.

How do I deal with air in the system?

Air causes a range of problems in pumps and can ultimately damage or break the pump. The best way to prevent air getting into the pump is to ensure that a flange is fitted on the hot water cylinder. Salamander sell an ‘S’ flange, which is a device used to remove air intake from the hot water cylinder from where the pumps draws hot water. The ‘S’ flange sits on top of the hot water cylinder and will need to be installed by a competent and trained installer. Click here for further information on the S falnge.

Most of our pumps must have a flange fitted to ensure longevity of life of the pump and for the warranty to remain valid. Click here for further information and exceptions to this.

Please ensure that the pumps’ warranty and installation guide book is checked before pump installation.

There appears to be no or significantly reduced pressure to my shower. What can I do?

If the pump is activating but there is still low/no pressure to the shower this is likely caused by a restriction after the pump, this could be:

Blocked filters – these are found on the inlets to the pump. Click here to find out how to clean them.
Shower head is partially blocked with limescale.
Twisted hose to the shower head.
Possibly the wrong pump has been installed e.g. you have a positive head pump but there is not enough natural flow, so you need a negative head (universal) pump. Click here to find out the difference between positive head and negative head systems.

The pump is delaying in activation? What could be the cause of this?

If the pump is slow to switch on it could be because there is something restricting the flow of water. This could be:

Blocked filters – these are found on the inlets to the shower pump. Click here to find out how to clean them.
Shower head is partially blocked with limescale.
Twisted hose to the shower head.
Possibly the wrong pump has been installed e.g. you have a positive head pump but there is not enough natural flow so you need a negative head (universal pump). Watch the video to find out the difference between positive head and negative head.

The pump is running but is not pumping any water, what should I do?

When a shower pump starts to display any of the following, an ‘open-ended’ test can be carried out to check that each side of the pump is functioning as it should:

Low pressure on hot, cold or both sides of the pump

Hot, cold or both sides of the pump will not activate.

Watch our video to learn how to carry out the open-ended test.

My shower pump works fine on one setting, such as hot or cold, but when mixed its pulses on and off. How can I resolve this?

When a shower pump starts to lose pressure or stops activating on hot or cold water, then turning the pump around can help diagnose the problem.

Watch our video on turning the pump around.

This is usually down to the natural flow of water, either the hot or the cold supply of water is not generating enough flow to activate the individual flow switches. Salamander Pumps require 2 litres per minute per side to switch on.

If this is a persistent problem it may mean that you need a universal pump. You can upgrade your shower pump to a universal shower pump by contacting Salamander Pumps.

My pump remains on even when the shower is switched off. What could be the reason for this?

Universal (Negative Head) Pump

If your pump has a pressure vessel, then the most likely cause for the pump running is that there is a leak somewhere in the system (like a dripping tap or shower, or slow pipework leak).

The easiest way to test if this is a pump issue or a leak, is to close the isolation valves on the outlet couplers (hoses) connecting the pump to the pipework. If you have a twin pump, you will need to close the outlet isolation valves on both ends of the pump.

If the pump continues to run after isolation valves on the pump outlets are closed, then it is a pump issue and you need to contact our technical desk either by calling 0191 516 2002 or emailing: tech@salamanderpumps.co.uk

If the pump does not turn on when the outlet isolation valves are closed, but does when opened, a weep/leak on associated pipework after the pump may be causing the pump to turn on with no demand.

Positive Head Pump

If your pump doesn’t have a pressure vessel and is a positive head pump then use the isolation valves as shown above to switch the water to the pump off.

If the pump turns off then there is a chance that water is going to somewhere in the system that it shouldn’t be e.g the vent pipe or cold water tank.

If this isn’t the case then contact our technical desk either by calling 0191 516 2002 or emailing: tech@salamanderpumps.co.uk

The shower pump keeps stopping and starting when no showers or taps are turned on, what should I do?

If the pump is positive head (doesn’t have a pressure vessel) and is turning on and off during use, this is most likely due to the amount of water coming into the pump not being enough to make the pump kick in. Positive head require 2 litres per minute (L/min) per side to activate so it might be that the flow is stopping and starting. Watch our video to learn how to measure water flow rate – this will help to determine if the system has the necessary flow rates for a positive head pump.

A negative head (universal) pump is indicated by a pressure vessel (as shown in the picture). These pumps turn on when they sense a pressure drop in the system. A dripping tap or leak in the system can cause the system pressure to drop which would activate a negative head pump, even though all outlets are turned off. This is called ‘hunting’. When a pump is ‘hunting’ you will hear the pump switch on for a few seconds when no outlets are open.

An isolation test will help to determine if a leak in the system is causing the pump to hunt. Watch our video to learn how to carry out an isolation test.

If the pump turns on while the outlet isolating valves are turned off, then it could be down to low or no pressure in the pressure vessel. Watch our video to learn how to check the pressure vessel – you will need a flat head screwdriver, and a foot pump with a gauge to carry out the test.

The shower pump has stopped working/ has low pressure, what should I do?

When a shower pump starts to display any of the following, an ‘open-ended’ test can be carried out to check that each side of the pump is functioning as it should:

Low pressure on hot, cold or both sides of the pump.
Hot, cold or both sides of the pump will not activate.

Watch our support video to learn how to carry out the open-ended test

My positive head shower pump will not start, what should I do?

A positive head pump requires a minimum flow rate of 2 litres per minute (L/min) to pass through the pump and out of the outlet, such as a tap or shower. 2L/min of both hot and cold water is required to turn on. If the flow rate is not at or above 2 L/min then the shower pump will not start. Click here to learn how to measure the flow rate.

Reasons why a positive head pump will not turn on:

There isn’t enough water flow to activate the pump, in this case a negative head (universal) pump should be installed.
A blocked or scaled shower head is restricting the water flow.
A twisted or damaged shower hose is restricting the water flow.
There is no electricity to the pump.
Debris in the filters to the pump, stopping the water flow. Click here to find out how to clean filters.

Watch our video to learn what to do when a positive pump will not turn on.

The pump keeps blowing the fuse or tripping the breaker. What should I do?

Unfortunately, this usually means that the pump has seized. Please contact our technical team on 0191 516 2002 or email tech@salamanderpumps.co.uk for further advice.

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