Poor Hot Water Flow - Buy a 40psi Jabsco Par Max 4??

[MtB]

5 minutes ago, Tony Brooks said:

What I find strange is that you say the outlet volume drops to very little before the pump comes back on on each pump cycle.

 

I hadn't noticed this. Given it doesn't happen on the colds supplies this suggests to me either there is a partially blocked strainer on the inlet of the water heater, or the water heater is suffering from scale contamination in the heat exchanger.  Fitting a pressure gauge to the inlet of the water heater would be a Good Idea. I have one on my Morco and it is revealing how wide the difference in pressure between the pump cut-in and cut out pressures. Pump cuts out at about 2bar and drops to about 1.2bar before cutting back in. (Water heater still works though!) It would be helpful to find out the pump cut-in pressure measured at the water heater inlet.

A tee in the water pipe just before it enters the water heater with one of these in the tee:

https://www.ebay.co.uk/itm/Pressure-Gauge-50mm-Dial-1-4-BSPT-Horizontal-0-15-30-60-100-160-300-PSI-Bar/132277427405?hash=item1ecc595ccd:m:mkFuczxMcu2jeRh_0v4MG1Q

[Tony Brooks]

58 minutes ago, Mike the Boilerman said:

 

I hadn't noticed this. Given it doesn't happen on the colds supplies this suggests to me either there is a partially blocked strainer on the inlet of the water heater, or the water heater is suffering from scale contamination in the heat exchanger.  Fitting a pressure gauge to the inlet of the water heater would be a Good Idea. I have one on my Morco and it is revealing how wide the difference in pressure between the pump cut-in and cut out pressures. Pump cuts out at about 2bar and drops to about 1.2bar before cutting back in. (Water heater still works though!) It would be helpful to find out the pump cut-in pressure measured at the water heater inlet.

A tee in the water pipe just before it enters the water heater with one of these in the tee:

https://www.ebay.co.uk/itm/Pressure-Gauge-50mm-Dial-1-4-BSPT-Horizontal-0-15-30-60-100-160-300-PSI-Bar/132277427405?hash=item1ecc595ccd:m:mkFuczxMcu2jeRh_0v4MG1Q

I agree with all of that. Its seems that across the whole range of modern domestic water pumps the cut in pressure is close to half the cut out pressure and I suspect that difference is too large for the best operation of things like instant gas water heaters.

[Richard10002]

On 04/11/2017 at 13:41, Tony Brooks said:

I agree with all of that. Its seems that across the whole range of modern domestic water pumps the cut in pressure is close to half the cut out pressure and I suspect that difference is too large for the best operation of things like instant gas water heaters.

Sorted!! 

My perception of the Jabsco Par Max 2.9 pump was that the pressure switch is not adjustable, and Jabsco actually state that trying to alter the pressure would invalidate their warranty.

Googling, I found a "High Pressure" Par Max 2.9, and a facility to buy the related pressure switch separately for about £26... however, for some reason, I got to the checkout clicked to buy, and the page hung, so I gave up. The High pressure pump cuts out at 40psi and cuts in at 20psi.

A bit more googling and I find that there is a screw on the pressure switch that adjusts the pressure. It is revealed by removing the blue pressure switch cover. Turning it clockwise increases the pressure at which the pump cuts in and out so, with the kitchen tap turned to hot, I turned the screw in quarter turn increments to the point where the flow of water increased to a reasonable level, the pump runs almost continuously, the Rinnai gas flame is lit continuously whilst the water is running, and the water is hot. bathroom hot water is fine, and the shower continues to work OK, so all is well

I dont know what I have increased the cut in and cut out pressures - I just increased it until it did the job. A benefit of the increased pressure is that the toilet has a more powerful flush - which is helpful

Thanks for all the info, advice, and discussion - without it I dont think I would have persisted to the outcome!!

[cuthound]

Thanks for bringing us up to date. Glad you got it sorted.

With the more powerful flush it sounds like you have invented a toilet and bidet combined  Bizzard will be most impressed.

[Tony Brooks]

Is best to check the pressure, a car type pressure gauge on the accumulator/expamsion vessel should tell you once the system is up to pressure and the pump turned itself off. The instant gas heater may have a maximum pressure for the heat exchanger.

[smileypete]

Thanks for the update, glad it's an easy fix.

Looks like I was reading too much into the workings of the flow regulator in the Rinnai, live and learn.

[Richard10002]

15 hours ago, Tony Brooks said:

Is best to check the pressure, a car type pressure gauge on the accumulator/expamsion vessel should tell you once the system is up to pressure and the pump turned itself off. The instant gas heater may have a maximum pressure for the heat exchanger.

From the installation manual: Water pressure must be between 0.23 and 7.0 bar. Pump must be capable of delivering 10 litres per minute. I'll try and remember the pressure gauge one day next week just to be on the safe side.

[Tony Brooks]

Its almost certain it will be fine, 7 bar is over 100psi.