I have central heating but no hot water

[King Ming]

My central heating is working, but I have no hot water.


My boiler is an ideal logic heat 15. I have hive active heating.


When I turn the central heating on in the Hive app, the hive receiver calls for central heating and the boiler fires up. It is working correctly.


When I turn the hot water on in the Hive app, the hive receiver calls for hot water but the boiler does not respond. It remains in standby mode.


I read online that the issue may be a problem with the 2/3 motorised valve in the airing cupboard. Mine is a danfoss hsa3. So I just bought a new one and replaced it like for like. But the issue remains.


Any advice welcome.

 

[stem]

Have you tried manually turning the hot water on using the button on the Hive receiver? Does it work then? If yes, the system is OK, the problem is with the Hive app or communication. If the light on the receiver comes on and it still doesn't work then there is a fault with the heating system or wiring.

Has the hot water ever worked since the Hive was installed? and if not, was it working before the Hive was installed?

The Danfoss HSA3 is a 3-Port motorised valve, so when there is a demand for hot water the boiler is actually controlled by the hot water cylinder thermostat and not the motorised valve, so assuming the hot water system was working correctly and has suddenly failed without anything being changed, my first port of call would be checking the operation of the hot water cylinder thermostat. It's quite easy for someone competent with using a multimeter to check.

 

[King Ming]

Thank you for reply, really helpful.

The hive has been installed for about three years and hasn’t skipped a beat. This issue only started yesterday.

Before I replaced the Danfoss HSA3 today, I yesterday moved it in to manual mode and this seemed to make the boiler respond correctly to hot water demand (though it was intermittent - I boost the hot water for 30 minutes but the boiler went back in to standby after about 20). This is why I thought it might be that Danfoss unit that was faulty. But today I replaced it for a brand-new one and the issue is the same.

As for the cylinder thermostat, it has been on 60° permanently but yesterday, at around the same time I put the Danfoss unit into manual mode, I turned the thermostat up to 70° and I noticed that the temperature of the hot water increased. So, does this rule out an issue with the cylinder thermostat?

 

[stem]

Sorry, I'm missing something here.

I thought that you said you had "no hot water" now you say "I turned the thermostat up to 70° and I noticed that the temperature of the hot water increased"
So I don't understand what the problem is. If the hot water cylinder is already hot, then the boiler won't respond when you switch the hot water on at the Hive.

 

[King Ming]

Sorry, I did not explain properly.

Yesterday I read online that, if the 2/3 motorised valve is not working properly, a way to override it is to slip it from auto into manual.

I did this and sure enough the boiler responded to the demand for hot water. This is what made me think that my Danfoss motorised valve was faulty. So today I replaced it for a new one like for like but the issue remains.

 

[stem]

Yes but I don't understand what the problem is?

My central heating is working, but I have no hot water.

OK. so you don't have any hot water.

I turned the thermostat up to 70° and I noticed that the temperature of the hot water increased.

Oh but you do have hot water

So what's the problem?

 

[stem]

Sorry I re read your comments you have hot water when in manual, but not in auto.

In manual, the valve is fixed with all ports open so thermostatic control of the hot water is overridden and the water will just get hotter.

Put it back in Auto, and switch the heating off and have only the hot water on. Then turn the cylinder thermostat up to maximum manually, you should hear a click and the boiler should come on.

Then turn the thermostat back down, again there should be a click and the boiler should go off.

 

[King Ming]

The problem is that the boiler only responded to demand for hot water after I slipped the Danfoss unit into manual.

This is why I assumed that it is the Danfoss unit that is faulty. However, after I changed it for a brand-new one today, like for like, the issue still remains.

In summary, when the Danfoss 3 motorised valve is in auto, the boiler is ignoring a demand for hot water. But when I slip that unit into manual, the boiler does respond to hot water demand.

 

[King Ming]

Our posts seem to have crossed. But I read your reply, thank you. I will try what you have said and report back. Thanks again.

 

[King Ming]

Good morning.


Today I had a hot shower.


Here is a summary of events:


Before I went to bed I set the CH to be off all night. That is, set not to call for CH at all.


The HW was timed to come on from 06:00 - 06:30. It did. The call for HW was made, the boiler responded correctly and hot water was produced. Perfect.


We consumed all the hot water and made sure it was all used by opening the HW tap and confirmed it as running cold. CH is still off. In the airing cupboard, all the copper pipes in the picture (prev post) are cold. So everything is now cold, as it should be.


Next, I used the hive app to turn on the CH, the call for CH was made, the boiler fired up, CH initiated. In the airing cupboard, the A and the AB pipes are warm, the B pipe is cold. That’s looking good and tells me the newly fitted Danfoss 3 way motorised valve is working correctly, feeding the CH but not the HW, as per current demand.


15 minutes later, I felt all the rads. They’re hot. I opened the HW tap to test and water is cold, as expected. I used hive app to boost HW for 30 minutes. Checked hive received connected to boiler, it’s now calling for HW as well as CH. Looking good. Up in the airing cupboard, All copper pipes now hot. 30 minutes later, HW tap runs hot.


So I’m tempted to now say, issue resolved and everything is now working as expected. Thank you for your valuable help. As you can probably tell, I’m no expert in this area - but I want to learn.

 

[MeldrewsMate]

Loose connection in junction box?

@stem, the Danfoss three port valve is different from the Honeywell in that it makes the end-switches when in the manual position, therefore the OP could have made the 'demand for heat' output even if the cylinder-stat was not calling for heat on HW only.

OP, if you have changed the three-port valve head then you should be capable of turning off the power to the system. I suggest you do this, then check the security and tightness of all wirig to the junction box, especially those (3 wires) going to the hot water cylinder-stat. Then check the connections at the stat too, before switching back on.

OP, if the Hive CH output is on, the room thermostat must also be calling for heat before the boiler will show 'c'. Otherwise it will show '0'.
Likewise if the HW output is on, the cylinder-stat must be calling for heat to bring the boiler on.