@porthy, not sure what is going on.  Is the water definitely heating up?  Is it going cold or just running out, i.e. it is only heating a small amount?  An ASHP can't heat water and do heating at the same time so you don't have to set timers like you have.  I don't know if it's possible for an ASHP system to somehow use the HW for the radiators; maybe one of our resident heating engineers could say?

I just leave my HW on 24/7 and it comes on when it needs to; if the heating is on at the time it overrides it.  There are various settings that control how that works. THe HW tank doesn't lose a lot of heat so that's not as wasteful as it sounds.

What make of ASHP have you?

Posted by: @porthy

Hi,  like many newbies to the world of ASHP, I’m floundering.  I’ve set the timer to heat the DHW and when this is done the central heating is set on timer to start warming the radiators up.  Problem is by the time someone needs a shower, the hot water has “disappeared”.  Yesterday the DHW, with the help of the Iboost had reached maximum temperature.  The heating then came on and a short time later the DHW was cold.  Where am I going wrong?  Any thoughts will be much appreciated? Thanks.

It is very simple, you are treating your heat pump in the same way as your old boiler, your het pump probably produces 5-12 Kw, Your old boiler probably produced 30-40 Kw. Therefor to produce the same ammount of hot water, your heat pump will take 5-10 times longer. You no longer own a boiler, you own a heat pump, you need to chainge the way you work with it if you want it to work.

The best way to do it is to stop trying to time it and allow your heat pump to controwl your hot water and just top it up uf necessary. The new cylinders only loose about 1 Kw of heat per day, not worth worrying about as the heat in to the house anyway.

If you want high energy bills and poor performance on a heat pump, use timers, third party thermostats and zone your property. All good heat pumps will be able to control the house tepmerature without intervention.

Posted by: @porthy

Hi,  like many newbies to the world of ASHP, I’m floundering.  I’ve set the timer to heat the DHW and when this is done the central heating is set on timer to start warming the radiators up.  Problem is by the time someone needs a shower, the hot water has “disappeared”.  Yesterday the DHW, with the help of the Iboost had reached maximum temperature.  The heating then came on and a short time later the DHW was cold.  Where am I going wrong?  Any thoughts will be much appreciated? Thanks.

Hi Porthy,

Welcome to the forum.

As Brendon has stated, it could be that you are just not heating the water for long enough, or it could also be that when the central heating is switched on, cooler water is being pumped through the coil in your hot water tank and actually cooling the water in the tank.

Without knowing the actual layout of your system and the actual timing and temperatures that are experienced it is difficult to give definitive advice. You could try the following test, switch on your central heating and raise the indoor temperature to 1C above your normal desired temperature, then switch off your central heating and switch on your DHW heating and monitor how quickly the water in the tank is heated. When the water in the tank is up to temperature switch off the DHW heating, but do not switch on your central heating. Monitor the rate at which the water in the tank cools. When the indoor temperature falls to a level at which you feel uncomfortable, then switch on the central heating and continue to monitor the water temperature in the tank. Whilst you are doing this note the operation of the control valves within your system.

If you find that the water in the tank cools more rapidly when the central heating is operating, it would indicate that one of the control valves may not be operating correctly.

As Brendon pointed out, ASHP's perform at their most efficient when they are operated continuously at lower water flow temperatures. Switching them on and off via timers is not the best way to operate an ASHP.

Posted by: @porthy

Hi,  like many newbies to the world of ASHP, I’m floundering.  I’ve set the timer to heat the DHW and when this is done the central heating is set on timer to start warming the radiators up.  Problem is by the time someone needs a shower, the hot water has “disappeared”.  Yesterday the DHW, with the help of the Iboost had reached maximum temperature.  The heating then came on and a short time later the DHW was cold.  Where am I going wrong?  Any thoughts will be much appreciated? Thanks.

It might be worth checking that the zone valve connected to your hot water cylinder is closing properly when the heating is turned on. Given the lower flow temperature of the heating it could cool the tank but would likely still be Luke warm I.e. same temp as rads c40c

Hi Porthy,

I have just had another thought about your problem.

Much depends on what control valves you have installed on your system, how they are being controlled, and whether they are functioning correctly. Also of importance is how you are switching your system on and off via the timer.

You can correct me if I am wrong, but I suspect that your system will have a circulating water pump in addition to the one inside your ASHP.

The circulating water pump is used to pump the heated water coming from your ASHP around the system within your home. When hot water is selected, the pump should push the water from your ASHP through the heating coil located in your hot water tank, normally via an on - off or diverter valve. Heat energy is therefore transferred from your ASHP to the water in your hot water tank.

When central heating is selected, the same circulating water pump pushes the heated water from the ASHP through the radiators and/or UFH pipes. It should not be pushing this heated water through the heating coil in the hot water tank at the same time.

If you are switching off your ASHP, but it is still possible for the circulating water pump to be switched on and off by the control system, then it is possible that this pump is pushing the 'no longer heated' water around the system, which could in fact have a cooling effect on the hot water in the tank.

I suggest that you check when the circulating water pump is running and when any installed valves are operating.

@kev-m thanks - I’ll leave the water on constant and see if that helps.

@kev-m I left the DHW on constant, but this morning the CH would not come on until I’d put the DHW’s timer back to auto, after which the internal pump kicked in to action and on the ASHP’s remote control I saw the symbol of a sun to signify call for heat and the symbol for the ASHP’s pump too, but no compressor or fan symbols.  Any thoughts appreciated.

@derek-m I left the DHW on constant all night, but this morning the CH would not come on until I’d put the DHW’s timer back to auto, after which the internal pump kicked in to action and on the ASHP’s remote control I saw the symbol of a sun to signify call for heat and the symbol for the ASHP’s pump too, but no compressor or fan symbols. I suspect it could be port valve problems.  After half an hour of CH, my wife took a shower, but the DHW was chilling speedily - she was not happy! Any thoughts appreciated.

@porthy Hi Porthy,

First of all look on the bright side, 'it could have been you taking the shower'!!!

Joking apart, how long have you had the system installed? Could you please provide a list of the installed equipment (manufacturer and model) and if possible a brief description of how it is connected/wired together.

From your overnight test there could be several routes to explore.

I am wondering if this isn't another problem.

1. Have you checked where the thermometer on the tank is? If its at the top that could be your issue as the top heats first. Moving it to the middle, or even bottom of the tank would solve this issue
2. Where is the cold water entering the tank? It should be at the bottom, but have you confirmed that?
3. Finally you say "maximum water temperature" but you haven't stated what that actually is? You might have a nice warm tank of 50 degree water, but add in some mains cold at 15 degrees and it'll chill pretty rapidly. upping your overall tank temperature would combat that.

@batalto thanks for your thoughts.  There are two thermostats connected to the thermal store - one towards the top and another towards the bottom.  Both are set at 65 degrees C currently.