Positive Head vs Negative Head Shower Pump — Which Do You Need?
A shower that won't pump properly can be incredibly frustrating, especially when you've invested in a new pump only to find it won't switch on. The culprit is often a mismatch between your system's water pressure characteristics and the type of pump you've chosen. This is particularly common in homes with loft conversions, bungalows with low-slung storage tanks, or properties where the cold water tank sits in an awkward cupboard rather than overhead. The good news is that diagnosing which pump you actually need is straightforward once you understand how water pressure works in your home. This guide walks you through the difference between positive and negative head pumps, how to measure your system, and how to avoid the costly mistake of fitting the wrong one. If you're at all uncertain after reading this, a qualified plumber can confirm your setup in minutes.
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Most likely cause & what to check
A positive head pump suits systems where the shower outlet is at least 300mm below the base of the cold water storage tank. The weight of water above creates enough pressure (a positive 'head') to automatically trigger the pump when the shower is opened.
A negative head pump (sometimes called universal or negative/positive) is needed when the shower is at the same level as the tank or higher — for example in a loft conversion, or where the tank is in a low cupboard. These use a more sensitive electronic flow switch that detects the tiny pressure change when the shower opens.
To measure: find your cold water tank in the loft. Measure the vertical drop from the bottom of the tank to your shower head. More than 300mm drop = positive head pump. Less than 300mm, or the shower is at the same level = negative head pump.
Using a positive head pump on a negative head system is a very common mistake — the pump simply won't start as there isn't enough initial flow to activate it.
Main UK brands offering both types: Stuart Turner (Monsoon Standard for positive, Monsoon Extra for positive/negative), Salamander (CT Force positive, Right Pump for negative), Grundfos (SB range), Aqualisa (Aquastream range). Always check the specification sheet before buying.
If you're unsure, a plumber can check your system and recommend the correct pump.
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Frequently asked questions
Why won't my new shower pump start when I turn on the shower?
The most likely reason is that you've fitted a positive head pump to a negative head system — or vice versa. A positive head pump relies on a minimum water flow to trigger itself, which won't happen if your shower head is too close to (or above) your water tank. Fitting the wrong type is one of the most common mistakes homeowners make.
What's the difference between positive and negative head shower pumps?
Positive head pumps need at least 300mm of water height above the shower to generate enough pressure to switch on automatically. Negative head pumps have sensitive electronic sensors that detect even tiny pressure changes, making them suitable for loft conversions or low tank positions where the traditional method won't work.
How do I measure whether I need a positive or negative head pump?
Locate your cold water storage tank and measure the vertical distance from its base to your shower head. If it's more than 300mm below, a positive head pump will work; if it's less than 300mm or the shower is at the same level or higher, you'll need a negative head pump.
Can I use a negative head pump if I actually have positive head?
Yes — negative head pumps (also called universal or dual-function pumps) will work on both positive and negative systems, though they're generally more expensive and sensitive to settings. However, using a positive head pump on a negative head system simply won't work and is money wasted.
My shower pump keeps cutting out — could it be the wrong type?
Possibly, especially if it's intermittent. However, intermittent operation can also indicate a faulty pump, airlocks in the system, or a blocked filter — a qualified plumber should diagnose which issue you're facing before you buy a replacement.
Is it a DIY job to fit a shower pump?
Physically installing a pump can be done by a confident DIYer, but diagnosing and selecting the correct pump type requires a good understanding of your plumbing system. If you're unsure, it's worth paying a plumber to check first — it'll save you money on buying the wrong pump twice.