Nest and hot water tank - help

41
Posted 14th Feb 2019
Hi guys

I'm wondering if someone can help me.

I have a megaflo tank, Worcester boiler and the nest heating hot water set up.

What in the cahoonas do I do in settings if I simply want the water in the tank to be heated as and when the temp drops in the tank.

I've tried to set the schedule 24/7 as in theory, the boiler would kick in everytime the temp drops. But the pump which is connected to the tank, that is linked to the nest heat link and that seems to then stay on all the time, instead of disconnecting.

It's driving me bonkers
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When I said pump I meant the motorised red valve.
Should there be a connection between the motorised valve and the thermostat in the tank?

That's the only thing I can think of, that the temp is bring reached but the valve does not know hence stays on?
Your hot water zone valve will open if the following is satisfied, in this order:

Call for hot water from the Nest - call for hot water from the cylinder thermostat - 230v to the brown wire of your zone valve.

If the hot water zone valve has opened correctly it then operates a microswitch that tells both the pump to come on, and the boiler. (230v on the orange wire of the zone valve).
themorgatron14/02/2019 19:43

Your hot water zone valve will open if the following is satisfied, in this …Your hot water zone valve will open if the following is satisfied, in this order:Call for hot water from the Nest - call for hot water from the cylinder thermostat - 230v to the brown wire of your zone valve.If the hot water zone valve has opened correctly it then operates a microswitch that tells both the pump to come on, and the boiler. (230v on the orange wire of the zone valve).


My issue is that when I put it on 24/7 schedule, theoretically the hot water should be heated until it reaches temp at which point, the tank thermostat tells the heat link I've reached temp, and the heat link tells the motorised valve to switch off.

Issue is that whether the tank is reaching temp (or not) its not communicating with the heat link and valve to stop.

I've tried it with the rads and they work perfectly. Set the temp to 20 and valve comes on, when the room stat reaches 20, her link tells the valve to switch off which it does, once temp falls below 20, it auto switches on etc.

Think the wiring from the tank, to the heat link must not be right. Only think I can think of.

Guy I've used is a fully qualified heating engineer who has fitted 100s of nest system with tank.

Hopefully just a obvious error.
themorgatron14/02/2019 19:43

Your hot water zone valve will open if the following is satisfied, in this …Your hot water zone valve will open if the following is satisfied, in this order:Call for hot water from the Nest - call for hot water from the cylinder thermostat - 230v to the brown wire of your zone valve.If the hot water zone valve has opened correctly it then operates a microswitch that tells both the pump to come on, and the boiler. (230v on the orange wire of the zone valve).


Does the hot water tank need its own heat link. I've only got 2, one for upstairs, one for downstairs. The hot water control has been connected to the upstairs heat link.
EN1GMA14/02/2019 19:59

Does the hot water tank need its own heat link. I've only got 2, one for …Does the hot water tank need its own heat link. I've only got 2, one for upstairs, one for downstairs. The hot water control has been connected to the upstairs heat link.


No, your set up should work fine.
EN1GMA14/02/2019 19:58

My issue is that when I put it on 24/7 schedule, theoretically the hot …My issue is that when I put it on 24/7 schedule, theoretically the hot water should be heated until it reaches temp at which point, the tank thermostat tells the heat link I've reached temp, and the heat link tells the motorised valve to switch off.Issue is that whether the tank is reaching temp (or not) its not communicating with the heat link and valve to stop.I've tried it with the rads and they work perfectly. Set the temp to 20 and valve comes on, when the room stat reaches 20, her link tells the valve to switch off which it does, once temp falls below 20, it auto switches on etc.Think the wiring from the tank, to the heat link must not be right. Only think I can think of.Guy I've used is a fully qualified heating engineer who has fitted 100s of nest system with tank.Hopefully just a obvious error.


Have you tried setting the Nest for hot water only, then "fiddling" with the hot water stat. You should be able to hear the clicking on/off, and usally hear the zone valve/pump moving.
Edited by: "themorgatron" 14th Feb 2019
themorgatron14/02/2019 20:00

No, your set up should work fine.Have you tried setting the Nest for hot …No, your set up should work fine.Have you tried setting the Nest for hot water only, then "fiddling" with the hot water stat. You should be able to hear the clicking on/off, and usally hear the zone valve/pump moving.


The valve for the hot water works, it's just a issue with the temp, not connecting to the heat link and valve.

If I switch off schedule, the valve will switch off. If I boost, the valve will switch on and switch off when boost time over

There's no physical stat on the megaflo tank which I think is stupid. How can you tell the temp....
themorgatron6 m ago

No, your set up should work fine.Have you tried setting the Nest for hot …No, your set up should work fine.Have you tried setting the Nest for hot water only, then "fiddling" with the hot water stat. You should be able to hear the clicking on/off, and usally hear the zone valve/pump moving.


Just switched off the schedule and the heat link acknowledges that, and in turn the motorised valve switches off.

Looking like a wiring issue between tank thermostat, heat link.

The tank thermostat is not communicating with the heat link to tell it ots reached temp, thus the heat link won't tell the valve to shut off
EN1GMA14/02/2019 20:03

The valve for the hot water works, it's just a issue with the temp, not …The valve for the hot water works, it's just a issue with the temp, not connecting to the heat link and valve. If I switch off schedule, the valve will switch off. If I boost, the valve will switch on and switch off when boost time over There's no physical stat on the megaflo tank which I think is stupid. How can you tell the temp....


The stat is hidden under the grey plastic box 1/3rd of the way up. Be aware there is live electrics inside.
themorgatron41 s ago

The stat is hidden under the grey plastic box 1/3rd of the way up. Be …The stat is hidden under the grey plastic box 1/3rd of the way up. Be aware there is live electrics inside.


There's definitely 2 wires connected there, 1 white 1 black
themorgatron14/02/2019 20:07

The stat is hidden under the grey plastic box 1/3rd of the way up. Be …The stat is hidden under the grey plastic box 1/3rd of the way up. Be aware there is live electrics inside.


Should the heat link connected to the water have how many wires connected. Mines only got 1 wire.
themorgatron14/02/2019 20:07

The stat is hidden under the grey plastic box 1/3rd of the way up. Be …The stat is hidden under the grey plastic box 1/3rd of the way up. Be aware there is live electrics inside.


One is for the electric heating element, the other I assume is for the boiler
EN1GMA14/02/2019 20:09

Should the heat link connected to the water have how many wires connected. …Should the heat link connected to the water have how many wires connected. Mines only got 1 wire.


The heat link connected to hot water has 1 wire (that goes to your hot water thermostat).
EN1GMA14/02/2019 20:10

One is for the electric heating element, the other I assume is for the …One is for the electric heating element, the other I assume is for the boiler


Correct!
Edited by: "themorgatron" 14th Feb 2019
How do you post a pic on a thread?
themorgatron14/02/2019 20:11

The heat link connected to hot water has 1 wire (that goes to your hot …The heat link connected to hot water has 1 wire (that goes to your hot water thermostat). Correct!


But the downstairs heat link, which is not connected to the water tank, has the exact same white wire.
EN1GMA14/02/2019 20:12

But the downstairs heat link, which is not connected to the water tank, …But the downstairs heat link, which is not connected to the water tank, has the exact same white wire.


There shouldn't be any in 4/5/6 of the downstairs heat link. He may have put it in before deciding which heatlink to use for hot water, then just left it isolated elsewhere at your wiring centre. Assuming it's not connected elsewhere it won't be doing any harm.
Edited by: "themorgatron" 14th Feb 2019
themorgatron8 m ago

The heat link connected to hot water has 1 wire (that goes to your hot …The heat link connected to hot water has 1 wire (that goes to your hot water thermostat). Correct!


I've followed the black thermostat wire from the tank and that is connected to a white rectangle box, brand same salus.

There's some sort of manual timer at the bottom of the set up like what you find on those oil radiators to set the timer.

Heat links have a white wire each, both going to the salus box.

I won't attempt it but I think connection may be loose on the thermostat wire on the tank
themorgatron3 m ago

There shouldn't be any in 4/5/6 of the downstairs heat link. He may have …There shouldn't be any in 4/5/6 of the downstairs heat link. He may have put it in before deciding which heatlink to use for hot water, then just left it isolated elsewhere at your wiring centre. Assuming it's not connected elsewhere it won't be doing any harm.


If I can work it out I'll try to post a pic.

Like I said, I think it's just a wiring issue but it's annoying
themorgatron4 m ago

There shouldn't be any in 4/5/6 of the downstairs heat link. He may have …There shouldn't be any in 4/5/6 of the downstairs heat link. He may have put it in before deciding which heatlink to use for hot water, then just left it isolated elsewhere at your wiring centre. Assuming it's not connected elsewhere it won't be doing any harm.


Thanks for the help and advice though, it really is appreciated. Thanks for the time
Edited by: "EN1GMA" 14th Feb 2019
The valve which is on the furthest right is the one for the tank

@themorgatron
You've got a low loss header so a bit different.

You should be able to trace the hot water as follows:

No 6. Heat link - No.1 cylinder stat - No.2 cylinder stat - live cylinder pump.

I would attempt to turn your cylinder stat down to it's lowest to see if that does shut off your pump.
themorgatron14/02/2019 20:30

You've got a low loss header so a bit different.You should be able to …You've got a low loss header so a bit different.You should be able to trace the hot water as follows:No 6. Heat link - No.1 cylinder stat - No.2 cylinder stat - live cylinder pump.I would attempt to turn your cylinder stat down to it's lowest to see if that does shut off your pump.


All the numbers you mention, no idea what you mean sir

Don't think I'm brave enough to mess with the stat on the tank whilst the thing is running....
EN1GMA11 m ago

All the numbers you mention, no idea what you mean sir Don't think …All the numbers you mention, no idea what you mean sir Don't think I'm brave enough to mess with the stat on the tank whilst the thing is running....


Maybe for the best! If you read the manual page 21-24 gives you an idea of how to adjust the thermostat. You still need to be vaguely proficient at wielding a screwdriver!
I now it's not the question you are asking but, if it's recently been installed isn't it really the engineer who installed it too come and fix the issues.

Why do you want the water too be heated all the time too a set temperature I thought the point of these things is that you can access the system from anywhere at any time or set it up so it can turn on and heat your water when you need it I would have thought heating it in the morning before you get up and later for teh washing etc would be best thing to do anyway.
MynameisM8 m ago

I now it's not the question you are asking but, if it's recently been …I now it's not the question you are asking but, if it's recently been installed isn't it really the engineer who installed it too come and fix the issues. Why do you want the water too be heated all the time too a set temperature I thought the point of these things is that you can access the system from anywhere at any time or set it up so it can turn on and heat your water when you need it I would have thought heating it in the morning before you get up and later for teh washing etc would be best thing to do anyway.


What I mean by heated all the time is that it auto heats to the desired temp when the tank gets filled with cold water when the hot water is being used.

So it wouldn't be on all the time per say, It just would not need to keep on boosting it manually. The 24/7 schedule would ensure it auto heats up if required.

We have a busy household, different times people get up, have showers etc so I need to ensure that hot water would always be available.

Sometimes people will have 2 showers, before work/school and after so lots of water is used. So scheduling will be difficult.
Have you spoken with the engineer what is he suggesting is it a fault. Or design fault just asking as I am considering too keep a hot water tank system in a property I have recently got usually it goest out and a combi is put in.
MynameisM2 h, 40 m ago

Have you spoken with the engineer what is he suggesting is it a fault. Or …Have you spoken with the engineer what is he suggesting is it a fault. Or design fault just asking as I am considering too keep a hot water tank system in a property I have recently got usually it goest out and a combi is put in.



Spoken to him and he's said try and increase the boiler temp. he suggested that if the boiler temp was lower than the tank temp then the heat provided will not reach the desired tank temp and thus it will remain on....made sense when he explained.

my tank temp is approx 70 degrees and my boiler temp was set to about 60 degrees (its a worcester boiler so number 4 on the dial).

he said try that because all the mechanics seem to work when i switch on/off without a schedule. either that or do as @themorgatron suggested and lower the tank thermostat and leave the temp dial as it is. either way, if the tank temp and boiler temp are off sync then theoretically ensuring they work in sync should cure the issue.
MynameisM15/02/2019 10:47

Have you spoken with the engineer what is he suggesting is it a fault. Or …Have you spoken with the engineer what is he suggesting is it a fault. Or design fault just asking as I am considering too keep a hot water tank system in a property I have recently got usually it goest out and a combi is put in.



my reasons for a tank were so that multiple people could use the hot water without losing pressure. i dont know if a tank saves significant amounts of money over a combi. but for ease of use in a family with different schedules, then the tank made sense.
MynameisM15/02/2019 10:47

Have you spoken with the engineer what is he suggesting is it a fault. Or …Have you spoken with the engineer what is he suggesting is it a fault. Or design fault just asking as I am considering too keep a hot water tank system in a property I have recently got usually it goest out and a combi is put in.


Unless you need the space you’d be daft to rip out a hot water cyclinder to replace with a Combi. As long as the cyclinder is suitably insulated and the boiler sized correctly it will be cheaper to run compared with a Combi.
EN1GMA15/02/2019 13:30

my reasons for a tank were so that multiple people could use the hot water …my reasons for a tank were so that multiple people could use the hot water without losing pressure. i dont know if a tank saves significant amounts of money over a combi. but for ease of use in a family with different schedules, then the tank made sense.


:/ I thought the pressure is worse on tank systems one.of the reasons I was considering too remove it.
paulj4815/02/2019 13:51

Unless you need the space you’d be daft to rip out a hot water cyclinder t …Unless you need the space you’d be daft to rip out a hot water cyclinder to replace with a Combi. As long as the cyclinder is suitably insulated and the boiler sized correctly it will be cheaper to run compared with a Combi.


Ok that's good then. I was under the same impression that it maybe possibly a bit more efficient in the summer as we have a tendency too run the hot water tap to wash hands but there's no real need for it as by the time.you have washed your hands the water has just heated up.and you close.it times that by 7-8 people 5-10 times a day and it probably adds up to too quite abit. Someone said too me if you have more than 2-3 taps the tank system is abit useless if that's not true all the better too keep it will save a good few thousand pounds.
MynameisM15/02/2019 14:07

Ok that's good then. I was under the same impression that it maybe …Ok that's good then. I was under the same impression that it maybe possibly a bit more efficient in the summer as we have a tendency too run the hot water tap to wash hands but there's no real need for it as by the time.you have washed your hands the water has just heated up.and you close.it times that by 7-8 people 5-10 times a day and it probably adds up to too quite abit. Someone said too me if you have more than 2-3 taps the tank system is abit useless if that's not true all the better too keep it will save a good few thousand pounds.


Trouble with a Combi is you need to size it for your domestic hot water requirements, this then is oversized for a typical central heating system, modern boilers can modulate the output down but there is still a minimum limit they can get too especially when TRV’s are shutting down and the demand reduces.
MynameisM15/02/2019 14:04

:/ I thought the pressure is worse on tank systems one.of the reasons I … :/ I thought the pressure is worse on tank systems one.of the reasons I was considering too remove it.


As far as I know, on a combi, you having a shower and someone turns on tap in kitchen, you going to be screaming at them to turn tap off

With the tank, multiple people have been able to have showers at the same time (in different showers in case you're thinking naughty thoughts ) and the pressure in each shower was spot on
EN1GMA15/02/2019 14:16

As far as I know, on a combi, you having a shower and someone turns on tap …As far as I know, on a combi, you having a shower and someone turns on tap in kitchen, you going to be screaming at them to turn tap off With the tank, multiple people have been able to have showers at the same time (in different showers in case you're thinking naughty thoughts ) and the pressure in each shower was spot on


Do you have some kind of a Extra pump fitted or just one that pumps water too the tank.
paulj4815/02/2019 14:13

Trouble with a Combi is you need to size it for your domestic hot water …Trouble with a Combi is you need to size it for your domestic hot water requirements, this then is oversized for a typical central heating system, modern boilers can modulate the output down but there is still a minimum limit they can get too especially when TRV’s are shutting down and the demand reduces.


I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with a tank. I am thinking too change rads too say 6 * (1400*600) doubles plus 2 * (1200*500) double and 2 smaller ones in bathroom and shower room not sure the sizes will this doo the job or need a bigger boiler.
MynameisM25 m ago

I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with …I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with a tank. I am thinking too change rads too say 6 * (1400*600) doubles plus 2 * (1200*500) double and 2 smaller ones in bathroom and shower room not sure the sizes will this doo the job or need a bigger boiler.


Have you done a heat loss calculation to get to that conclusion?
MynameisM32 m ago

Do you have some kind of a Extra pump fitted or just one that pumps water …Do you have some kind of a Extra pump fitted or just one that pumps water too the tank.


Not sure but I know there's at least a couple of pumps. It's a 4 storey house, 3 bathrooms, about 18 rads across the house so that water does need a pump to push it through
MynameisM30 m ago

I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with …I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with a tank. I am thinking too change rads too say 6 * (1400*600) doubles plus 2 * (1200*500) double and 2 smaller ones in bathroom and shower room not sure the sizes will this doo the job or need a bigger boiler.


What Paul said, use the calculators on radiator websites to give you an idea of what BTU you need for each room and go from there. It'll atleast be a guide.
MynameisM32 m ago

I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with …I need bigger sized rads it's currently got a 15kw. Glow-worm boiler with a tank. I am thinking too change rads too say 6 * (1400*600) doubles plus 2 * (1200*500) double and 2 smaller ones in bathroom and shower room not sure the sizes will this doo the job or need a bigger boiler.


With a combi, if the rads are on, and you switch on the hot water, then connection is lost with the rads whilst you're using the hot water. It connects back again once you stop the water.

With the tank, you can have rads on, and use water without losing either.

Unless you can get combis which do both simultaneously
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