Coldwater Accumulators - 1 not filling

[Skiddaw]

Hi,

First post, just joined in the hope someone may kindly be able to help with the problem as per the thread title. I will explain the setup:

On non mains water into holding tank then fed into house, into 2 accumulators via a Mainsboost charger. Been working fine for many years. During recent cold weather the external pipes/tank froze. This happens quite often due to being in an area which has very cold weather. Once defrosted everything normally kicks back in working. This time we received an error on the mainsboost charger saying it had failed. It had indeed failed and has now been replaced. So onto the issue, following the charger replacement, only 1 of the accumulators is filling. Plumber has checked everything he thinks and ST (Stuart Turner) tech help have been very helpful but to no avail.

Having tested the diaphragm in the vessel which is not filling, there is no water coming out of the schrader valve so the presumption is it is fine. All inlet valves are open to the vessel.

There has been lots of mentions of the vessel pressure. Today the readings for the 2 vessels were 0.95 bar for the one filling and 1.2 for the other one. The suggestion was to set the pressure to be the same for both which we have done. The mains pressure reading is 1.5 bar, so am I right in thinking the differential will mean the pressure on the vessels needs to be lower?

On setting the pressure on both vessels to 0.95bar and restarting the charger the same thing happened, only 1 vessel filled. If we shut off the inlet valve to the vessel which is filling and only leave the other one open, still no water goes into it. The charge continues running until the auto 180min cutout kicks in.

I really am hoping someone can help. Is there anything else, obvious or not, which is likely? We are in a very rural area and finding plumbers who can help is proving difficult. ST do not have any technicians anywhere in the county.

Many thanks in advance.

 

[Skiddaw]

If the vessels start out at the same pressure empty, then during the fill cycle they both increase pressure by the same amount, that would suggest they are both filling equally.
When you say 1 vessel is not filling, how are you determining that?

Highly technically (!), by tapping the side of the vessels, empty is hollow sounding, full does not sound hollow. An empty vessel also can be very gently rocked (we never do this!) a full one is much heavier and cannot be rocked if tried.

Prior to the charger change, when both vessels were full, the charger would switch off, from empty this would normally take no more than 20 mins. Currently the charger will run for a full 180mins before the auto cutout kicks in. I am presuming this is happening to try an fill the vessel which is not filling?

 

[Skiddaw]

Ok, another update which dare I say it a bit more positive, the first vessel now does seem to have some water in it (I think), the pressure readings are 2.3bar on both vessels - the same pressure showing on the charger.

Shall I let the charger just run, could it just be taking longer to fill them both than normal because they have both not been full for a while?

Thank you again for everyone's help.

 

[John.g]

Take it that you are taking pressures from both schrader valves, to increase the pressure from 2.3 to 2.8 bar will only require 72 litres, say 3 minutes, is the charging pump supplying the system normally as well, if so if the demand is close to the pump flow capacity of ~ 25 LPM then it could take hours to fill the accumulators.

 

[Skiddaw]

Yes both valves. So the hours to fill, because they were both very empty? Normally the charger does not run for any more than 20 mins when filling them both from empty. Apologies probably the same questions, I just trying to get my head around what may be happening having only changed one part of the system (the charger).

At least if both vessels are now filling it is more positive. I am hoping they will fill completly, the charger switch off and then as we use water in the house the charger kicks in as and when needed which is how it has always worked. The charger would only kick in if the demand was high.

This is the charger.

https://www.stuart-turner.co.uk/contentfiles/Mainsboost-Wall-Mounted-MBC-12-DS.pdf

 

[John.g]

The charger kicking in depends on its cut in pressure so if its set slightly lower than the (dynamic) mains pressure then will only cut in when both accumulators are empty. To fill both accumulators from 1.0 bar (empty) to 2.8 bar requires 426 litres of water so if the pump output is 25 LPM then 17 minutes to re charge, Still doesn't explain though why the pump was running continuously, the only logical explanation is that the demand was > 25 LPM or whatever the pump is rated at.
Have you any idea of the pump output or a link to it, for interest.

 

[Skiddaw]

The charger kicking in depends on its cut in pressure so if its set slightly lower than the (dynamic) mains pressure then will only cut in when both accumulators are empty. To fill both accumulators from 1.0 bar (empty) to 2.8 bar requires 426 litres of water so if the pump output is 25 LPM then 17 minutes to re charge, Still doesn't explain though why the pump was running continuously, the only logical explanation is that the demand was > 25 LPM or whatever the pump is rated at.
Have you any idea of the pump output or a link to it, for interest.

I have put a link to the charger on a previous post, I have the documentation here for it too, I am looking for the output but not finding anything currently. There are a number of settings for the charger which I can detail here and what they are set to?

Your calculations (thank you) seem to equate to the time the vessels used to take to fill prior to the charger change. So although further forward something still is not right. I have just checked again, everything still at 2.3bar, the vessels appear to be full (as far as I can tell) but the charger still running.

 

[Skiddaw]

The settings which can be changed on the charger are with current settings:

Set Point - 3 bar
Diff Pressure - 0.5 bar
Low Pressure - 0.2 bar
High Pressure - 4.5 bar
Pump Run Timer - 180 mins

The remainder are to do with the alarm settings

 

[John.g]

A set point of 3 bar with a diff. press of 0.5 bar would indicate to me that it cuts in at 2.5 bar and cuts out at 3 bar. I don't know what the low and high pressure settings refer to.
The pump data as you said gives no flow rate but the power consumption of 398 watts should by my calc give 20/25 LPM.

I think you have a problem with the new charger, could be something as simple as a bit of dirt under a non return vave, I don't think there was/is anything wrong on the accumulator side, I would get back on to your plumber & stuart turner. In the mean time you might consider reducing the setpoint to say 2.1/2.2 bar and then the pump shouldn't run continuously even though it is rated as such.

Only other thing I can think of is that it is pumping back through the mains due to a faulty NR valve (if) installed somewhere in your system (not the pump).

 

[Skiddaw]

A set point of 3 bar with a diff. press of 0.5 bar would indicate to me that it cuts in at 2.5 bar and cuts out at 3 bar. I don't know what the low and high pressure settings refer to.
The pump data as you said gives no flow rate but the power consumption of 398 watts should by my calc give 20/25 LPM.

I think you have a problem with the new charger, could be something as simple as a bit of dirt under a non return vave, I don't think there was/is anything wrong on the accumulator side, I would get back on to your plumber & stuart turner. In the mean time you might consider reducing the setpoint to say 2.1/2.2 bar and then the pump shouldn't run continuously even though it is rated as such.

The low and high pressure settings are the failsafe settings.

I have switched the charge off with the pressure at 2.3 bar as nothing more seemed to be happening, there is no doubt now both vessels are full.

Without sounding like I know too much, which I certainly do not, when I typed out the settings of the charger I wondered if I need to lower the 3 bar setting, you have kindly already answered. I will lower the setting now as you say which will at least allow me to use the system as planned and leave the charger switched on without constantly running.

I will speak to everyone tomorrow as you said and will come back and update, in the meantime thank you to you and everyone else for all your help, it is very much appreciated.

 

[John.g]

Very good, just to say it "cant" be any problem with a NRV in the mains as that is what is being boosted! so possibly NRV in the pump itself.

 

[Skiddaw]

Very good, just to say it "cant" be any problem with a NRV in the mains as that is what is being boosted! so possibly NRV in the pump itself.

Thanks John. I will get the plumber to check all the valves again, plus the charger as well as speak to ST.

I have changed the setting on the charger to 2.2 and thankfully the charger has stopped. Having also used some water since, when the pressure drop is higher than the 0.5 differential setting the charger automatically comes on.

Once again many thanks for all your help.

 

[Timmy D]

Good job John 💪🏻