I wrote this blog originally back in 2015 and I have been updating repeatedly in response to the very few customers who have had problems. Whilst pulsing pressure, pulsing temperature and/or pulsing flow is very rare, it is very annoying, but it can be solved if the reason can be identified. This blog is long because I wanted to cover all the reasons for pulsing even, if that reason was reported by just one of my previous 20,000 customers.
Flow and Temperature fluctuations are caused by the following:-
LACK OF WATER
A NEED TO BALANCE HOT AND COLD PRESSURES (Or Unbalance!)
To diagnose the problem and solve the problem a number of simple tests can help:-
Test one: Maximise water flows to check its not a capacity problem
Open taps to the maximum, take off shower heads, and with the pump running, run as much water through the pipes as possible.
1.0 If the pulsing continues whilst you are drawing maximum water, then your problem is lack of water. The lack of water might be caused by (1) Sediment in the bottom of a cold water tank (2) The valve between the cold water tank is corroded (3)The valve between the cold water tank and the bottom of the hot water cylinder is partly closed (turn anticlockwise to open) (4) There is scale in the bottom of your hot water cylinder. (5) The top exit fittings at the top of the cylinder are corroded.
With any of the above problems, water flowing though a hot water cylinder is limited, but the vent pipe fills with water when the pump is not running. The pump can draw water from the vent pipe but pumps water away faster than it accumulates. The pump with no more water to pump causes the rotor to spin in a water/air mix which is so inefficient that the water builds up again and then, when there is enough water, it pumps efficiently again, but soon runs out of water again.
The noise of the pump ramps up and down in pitch: pumping water is low pitch, pumping a water and air mix is a high pitch.
2.0 If the pulsing stops, then it is likely to be back pressure. Back pressure can be caused by a poorly designed shower head, a shower hose with an internal bore less than 10mm, restrictions in the shower or tap mixer, air in the pipes, or some other blockage in the pipes.
This first test is normally the best first test to do, because if you have back pressure and it is because of trapped air, the water moving as fast as you can make it move may carry the trapped air with it and after this test the problem may simply disappear.
Test Two: Check the hot water temperature.
1.0 Many mixers have ‘anti-scald’ prevention which closes the hot port to the mixer if it senses very hot water. The anti-scald can be over-sensitive to hot water, or not-so-hot water, and overcorrects by closing the hot port too much. In response to closing the the hot port too much, the water becomes too cold and so opens the hot port again, but overcorrects and the cycle repeats.
2.0 Lowering the temperature to say 55 degrees of even 50 degrees may stop the anti-scald needing to react.
3.0 Changing the temperature changes the water mix ratio, and the lower the temperature the higher the hot flow, and as a result the lower the hot pressure. The higher the temperature the lower the hot flow and so the higher the pressure. Changing temperature up or down will affect the dynamics and could give a sweet point which stops the pulsing.
Test 3 – Check the Power Supply
Check the socket and if necessary use an extension lead to bring power from another plug socket.
This blog gives you an example of why this may be important:-
Check the Shower Head and Shower Hose
If you have a pulsing pump, remove the shower head as this reduces the back pressure. If it stops pulsing then a WRightChoice shower head may be all you need. You can buy WRightChoice shower heads and hoses on this site.
Again, removing the shower head will have increased the flow in the pipes, which may have flushed out air in the pipes (another cause of pulsing). Refit the old shower head and if the pulsing has gone then job done.
Need For A Second Pump on the Cold
If none of the above helped then it could be that the mixer needs a more balanced hot and cold pressure; in a gravity hot and gravity cold system you need to add a SP2U to the cold if you were only boosting the hot.
Pulsing Pumps Caused By Mixer)
Mixers are less likely to pulse if you pump both the hot and cold, but for most a single pump on the hot gives good shower and the mixer does not pulse.
Many mixers which pulse at one temperature and pressure are fine if you change the temperature of the incoming water.
Thermostatic Taps and Shower Mixers.
There are three reasons that a tap or shower mixer may be causing fluctuating flows and/or temperature fluctuation. These are oversensitivity, the cassette sticking, and/or restrictions in the tap which causes back pressure.
Thermostatic Mixers have a cassette which may be oversensitive or sticking
A thermostatic mixer will try to balance hot and cold and will restrict the flow from the hot and the cold. When a mixer has not reached the temperature it wants, it will prioritise the hot port until hot water arrives. Once hot water arrives at the mixer it will reduce the flow on the hot port and increase the flow on the cold port to try to give the temperature you need. If the cassette is slow to act it may overcompensate and open the cold port too much and close down the hot too much, resulting in fluctuating temperature and pressure.
The degree of fluctuation is affected by temperatures, pressures, and differential pressures between the incoming hot and cold. The shower head and shower hose can also have a dramatic effect, and any single change can eliminate the problem.
Typically for thermostatic mixers, troubleshooting and maintenance guides will state their mixers will deal with differential pressure of 5:1; however SPB know from experience that some mixers do struggle and within the same brand, make, and model, some mixers cope, others do not.
I carried out a free service visit to a customer in Ely. He had a Bristan Shower Mixer and the hot overpowered the cold when he first fitted just a SP2B on the hot. He upgraded with a SP2U, but although the hot no longer overpowered the cold – it pulsed. We tried a SP1U on the hot to double boost the hot, whilst single boosting the cold and wow! We may never know why the mixer caused pulsing, but he was appreciative of his power shower and my reward was a 5 star review.
Back Pressure Caused by a Mixer Tap or Mixer Shower
The UK and Eire are uniquely different to the rest of Europe in that the UK and Eire allow a minimum of 1 bar pressure for incoming mains pressure and many properties have gravity systems. Despite this, major household brands sell shower mixers and taps based on the much higher mains pressures in say Germany and France. Obsessed with water saving, they put in many water restrictors and micro filters which have a purpose in France and Germany, but in the UK simple reduce the flows to an unacceptable degree.
All our ShowerPowerBoosters have filters, so I would argue that all filters and restrictors could be removed.
I have a customer who delighted in removing 4 filters and 4 flow reducers from his shower mixer to achieve Wow!
Pulsing Pumps due to Airlocks
Airlocks prevent the full effect of the pumps being received, as energy needed to increase flow and pressure is wasted in pushing air about. As the air moves the resistance to flow changes and this can cause pulsing.
This is a real report from a customer survey:-
January 14th 2015 – Mr Harrison – Wymondham Norfolk
Problem Reported – Pulsing pump
Reason For Problem
In order to feed the shower a 22mm pipe had been taken from a point near the hot water cylinder – up into the loft – across the loft – and down to the shower. This effectively trapped a column of air which had no way of being vented from the pipe installed.
Solution To Problem
Mr Harrison connected the pipe to the hot water vent pipe in the loft, with the pipe falling all the way to the shower, eliminating trapped air. I received this email just a couple of hours after I left him:-
Thanks for coming round this evening it was nice to meet you, I have changed all the pipework around and so far so good, we have had two showers and it hasn’t pulsed so looking good.
I like fitting these pumps now.
Check the filter in the tap spout and consider cleaning it or removing altogether.
If all else fails
Please contact one of our customer service team
Alan may be able to arrange a free service visit