Short version (TL;DR): how can I measure the output pressure of a water pump in a spa heating system and verify that it is within the gas heater input pressure specs?

The Whole Story

I'm trying to troubleshoot an outdoor spa heating system in my parent's home which is located in SW Brazil. Its simplified diagram is as follows:

Spa heating system diagram

(just replace the word pool by outdoor spa and remove the word filter and that's exactly what I have)

The heater is about 6m (20 feet) away (horizontally) and 1.5m (5 feet) above the pump.

The Pump

The pump picture and specs are the following:

enter image description here

  • Power: 220W
  • Input voltage: 220V AC
  • Frequency: 60Hz
  • Maximum temperature: 90ºC
  • Maximum pressure (suction/input): 60mWc (meters of water column) or 85psi
  • Maximum pressure (output): 12.5mWc or 17.8psi
  • Maximum flow: 58L/min
  • Connections: 1''
  • Weight: 5.0kg
  • Country of origin: Brazil

Product link: Texius TBHGF • 220W

The Gas Heater

The relevant gas heater specs and info are below:


  • Minimum water input pressure: 2.5mWc or 3.5psi

Product link (similar to mine, which is outdated): Orbis passage gas heater - model 315


The heating system was working properly until we noticed a significant decrease in the hot water flow coming into the spa and increase in its temperature. After a while, the heater would turn off even with the pump turned on. Now the heater won't even start (it won't even make the sparks that light up the gas). I did replace the 1.5V D alkaline battery, but no joy.


  1. Assuming the problem is the reduced pump output pressure, how can I measure it to make sure it's really under the minimum heater input pressure?

    I am looking for solutions involving any of the following:

    • a DIY apparatus to measure the pump output pressure
    • clever ways to make measurements and physics equations to calculate the pressure
    • off-the-shelf measurement tools and gadgets (the cheaper the better, for occasional one-off measurements like in my case)
  2. Are there any other possible causes for this problem?


Well, I did try to ask Google this same question, but could not make any sense of the results. Maybe I'm not asking the question properly, or I'm not using the right keywords.

PS. I have converted the pressure units to PSI using ConvertTop.com - pressure.

  • 1
    You should be able to plumb a pressure gauge in between the pump and the heater.
    – Tester101
    Sep 6, 2014 at 19:26
  • 1
    ... and pressure gauges can be obtained at any plumbing supply store, and at least some home-handyman and hardware stores. They aren't expensive. How they'd install depends on the type of pipes you're dealing with.
    – keshlam
    Sep 6, 2014 at 21:11
  • @Tester101 - Great idea! I think I'm going to install a couple of them in strategic places.
    – Ricardo
    Sep 6, 2014 at 21:38
  • @keshlam - good to know. I'll get a couple of gauges and install them myself. Sounds like fun.
    – Ricardo
    Sep 6, 2014 at 21:43

1 Answer 1


Another solution might be to just buy and install a new pump. If that solves it, you're golden. If not, you now have a spare for when the pump does eventually die.

Obvious caution: Electricity and water. Be VERY sure of what you're doing when you make the connections and seal them up.

(I presume you've already checked the obvious -- made sure all valves are fully open, that any flexible pipes aren't kinked, and so on.)

  • I'll shop around and if a replacement isn't too expense I might just do that. Thanks! Also thanks for the warning. +1
    – Ricardo
    Sep 6, 2014 at 21:47

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