DHW Fluctuating Temperature - but not board or DHW sensor.

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DHW Fluctuating Temperature - but not board or DHW sensor. Empty DHW Fluctuating Temperature - but not board or DHW sensor.

Post  RG58 on Sun Mar 10, 2019 1:46 pm

For some years, we have used the Immersion Heater to keep the shower water temperature constant.  This has worked fine so long as we remembered to turn it off again immediately after using the shower!  Everything else has worked fine until the central heating decided to stay on intermittently in the autumn despite any instructions being received from the room thermostat.

So we bit the bullet and replaced the main PCB.  That fixed that fault so I have also now replaced the DHW sensor to try and cure the fluctuating water temp  It has made very little difference.  We can sometimes get away with it with one shower that has thermostatic controls but the fully manual one - hot and cold just as before so we are again resorting to using the immersion heater.

Some posts recommend changing the other sensor as well but what difference does that make to the DHW temp?  All readings seem ok on the main PCB display although frankly, I am not exactly 100% sure what I should be looking at!  From the manual, the various LED's seem to light up correctly but I don't really know where else to look.

The hot water pump has recently started to get noisy. One can hear it pulsing on and off whilst in the shower. Not sure if it is just a forewarning of it failing or could actually be the cause of the fluctuating water temperature. Any ideas?

RG58

Posts : 8
Join date : 2017-11-15

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Post  mike on Thu Mar 21, 2019 11:50 am

Both sensors the DHW & PHE are both ref the hot water.

Also check that the unit is full. Check header tank.

Check water can & will drain from doc near DHW pump. Cover pump with foil etc. Do not get wet!

Pump noise can be ref the above / a water problem

Or the pump is on it's way out.

Mike

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Post  RG58 on Thu Mar 21, 2019 8:19 pm

Thanks Mike. Can you explain why the PHE sensor would affect the domestic hot water please as that is one I have never changed? To change the DHW sensor all I did was to turn off the mains stopcock, release pressure by opening a tap and then just letting it cool down for a couple of hours before unscrewing the old sensor? Would I be right in saying it is a similar process with the PHE sensor except I assume I would have to release the pressure somewhere other than a tap?

Also, what do you mean by "doc near DHW pump" please? Would that be the drain plug I think I can see in the manual on page 6, just to the left of the PHE sensor, above the pump?

Thanks.

RG58

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Post  mike on Fri Mar 22, 2019 5:12 am

PHE sensor is there for a reason.

It tells the ACB the temperature of the dirty water in the unit going through the PHE (plate heat exchanger)

The DHW sensor is the hot water to the taps etc.

Using both sensors. The ACB then speeds up or slows the DHW pump to keep hot water 50 to 55c

To change PHE sensor

Switch unit off

Cover DHW pump with foil to protect from any water.

Turn off water to F & E tank. Drain out water using drain off near DHW pump.

Remove and fit new PHE sensor. Take extra care making connection to plug on ACB

Turn water back on to F & E and fill unit.

Check pump is full of water / no air.

Also put hose on the doc and make sure water is there and not air. Let it run if need be.

Switch on and check unit temperature. Run tap see how it goes.

It can be Pump trouble
Water trouble from the F & E tank to doc
I have even had a problem where the ACB was the issue (but rare)

All the above is easy to write and very often easy to do.

But there are pitfalls as with any job.

Mike

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