Hot water not heating
Discussion
Trying to get my head around this issue.. been going on since we moved in which was in September.
It only seems to happen every now and then, maybe once every 4 weeks or so.
I suspect its maybe a faulty zone valve?
Basically we have the following
Gas boiler with cylinder next to it.
2 zone valves, one for heating and one for cylinder.
The cylinder has a thermostat on it.
Boiler is set to flow at 67c. For testing purposes I have set the hot water tank stat to 70c.
The boiler will fire up, run to about 40c and then shut down.
Like its not detecting any flow maybe?
It seems to do this 2-3 times in a row then shuts off all together.
Today as a test I manually opened the zone valve and the boiler did its usual fire up but then slowly over time the temp rose ever so slowly to 60c.
It took about 10 mins for this to happen I have now left it to continue but will check it again shortly.
Is it most likely the zone valve?
I guess it could be the thermostat but its clicking with a nice positive sound. I took the cover off the junction box that sends it to the boiler to check for loose wires but all looks ok.
Boiler isn't particularly old, its a Valliant Ecotec 637.
Tank etc all installed at the same time I think its about 6 years old.
If you feel both sides of the pipes between the zone valves they do get hot but only in step with what the boiler says.
Maybe its clogged?
Or could this be a boiler issue?
It only seems to happen every now and then, maybe once every 4 weeks or so.
I suspect its maybe a faulty zone valve?
Basically we have the following
Gas boiler with cylinder next to it.
2 zone valves, one for heating and one for cylinder.
The cylinder has a thermostat on it.
Boiler is set to flow at 67c. For testing purposes I have set the hot water tank stat to 70c.
The boiler will fire up, run to about 40c and then shut down.
Like its not detecting any flow maybe?
It seems to do this 2-3 times in a row then shuts off all together.
Today as a test I manually opened the zone valve and the boiler did its usual fire up but then slowly over time the temp rose ever so slowly to 60c.
It took about 10 mins for this to happen I have now left it to continue but will check it again shortly.
Is it most likely the zone valve?
I guess it could be the thermostat but its clicking with a nice positive sound. I took the cover off the junction box that sends it to the boiler to check for loose wires but all looks ok.
Boiler isn't particularly old, its a Valliant Ecotec 637.
Tank etc all installed at the same time I think its about 6 years old.
If you feel both sides of the pipes between the zone valves they do get hot but only in step with what the boiler says.
Maybe its clogged?
Or could this be a boiler issue?
Have you got any restriction on the HW Tank coil inlet or outlet (Gate Valve)??
Valliant (and glow worm) boilers don't like it if the temp between flow and the boiler and return to the boiler exceeds 20 deg C - basically they shut down to protect the boiler.
You can create a situation where this happens by restricting the feed to the coil or the return from it - boiler ramps up and then as soon as it sees greater than 20 diff between flow and return it shuts down.
You can stop this by
1. Opening up any gate valve so the flow thro the coil is faster so the boiler see the return rise quicker
2. Range rating the boiler so it doesn't throw the full power of it at the HW coil
Valliant (and glow worm) boilers don't like it if the temp between flow and the boiler and return to the boiler exceeds 20 deg C - basically they shut down to protect the boiler.
You can create a situation where this happens by restricting the feed to the coil or the return from it - boiler ramps up and then as soon as it sees greater than 20 diff between flow and return it shuts down.
You can stop this by
1. Opening up any gate valve so the flow thro the coil is faster so the boiler see the return rise quicker
2. Range rating the boiler so it doesn't throw the full power of it at the HW coil
I think its that yes 20c because what I have noticed is if I turn on the heating, let it settle for a min then boost the water the zone valve opens and its happy.
You see about a 3c drop or so on the boiler and then it catches it and powers up a little and then settles back at the preset flow temp.
Now if you just boost the water on its own, so the zone valve to the heating is closed the temp shoots up to well over the preset flow temp and then it shuts off and you get the timer symbol for 5 mins.
Then it tries again. And again.... and after a while it just sits around 40c and does not budge, which I guess is maybe some sort of protection mode?
If at any point you command heating the zone valve opens and its happy as larry and hot water starts to flow to the cylinder too.
I was wondering if the zone valve was not opening causing this "backup" and thus cycling of the boiler.
Its hard to tell as our hot water comes on at 6am, so I think to test it out I will have to move this to in the daytime to really see whats going on.
Regarding taking the zone valve off.... is this easy to do?
You see about a 3c drop or so on the boiler and then it catches it and powers up a little and then settles back at the preset flow temp.
Now if you just boost the water on its own, so the zone valve to the heating is closed the temp shoots up to well over the preset flow temp and then it shuts off and you get the timer symbol for 5 mins.
Then it tries again. And again.... and after a while it just sits around 40c and does not budge, which I guess is maybe some sort of protection mode?
If at any point you command heating the zone valve opens and its happy as larry and hot water starts to flow to the cylinder too.
I was wondering if the zone valve was not opening causing this "backup" and thus cycling of the boiler.
Its hard to tell as our hot water comes on at 6am, so I think to test it out I will have to move this to in the daytime to really see whats going on.
Regarding taking the zone valve off.... is this easy to do?
gotoPzero said:
I think its that yes 20c because what I have noticed is if I turn on the heating, let it settle for a min then boost the water the zone valve opens and its happy.
Ahh if I understand that correctly - you are doing HW before the CH is on - that will make things twice as bad - the HW/CH circuits will be at their coldest temp having cooled down from the previous heating period.gotoPzero said:
You see about a 3c drop or so on the boiler and then it catches it and powers up a little and then settles back at the preset flow temp.
Now if you just boost the water on its own, so the zone valve to the heating is closed the temp shoots up to well over the preset flow temp and then it shuts off and you get the timer symbol for 5 mins.
Earlier you saidNow if you just boost the water on its own, so the zone valve to the heating is closed the temp shoots up to well over the preset flow temp and then it shuts off and you get the timer symbol for 5 mins.
gotoPzero said:
The boiler will fire up, run to about 40c and then shut down.
Like its not detecting any flow maybe?
It seems to do this 2-3 times in a row then shuts off all together.
Which is it?Like its not detecting any flow maybe?
It seems to do this 2-3 times in a row then shuts off all together.
1. shoots past set point and then shuts down
or
2. doesn't get to set point and hangs
The timer is probably "anticycle" Timer or Pump Over run timer - depends what you have parameter wise in the Boiler
gotoPzero said:
Then it tries again. And again.... and after a while it just sits around 40c and does not budge, which I guess is maybe some sort of protection mode?
Yep gotoPzero said:
If at any point you command heating the zone valve opens and its happy as larry and hot water starts to flow to the cylinder too.
Have you got a three port valve or 2 single zone valves?Either way with HW and CH both open the flow is shared but that also make me think that you probably do have a restriction to or from the HW coil. Water is lazy and takes the easiest path with CH and HW on together the water would normally prefer to pass thro the HW coil as it's closer and easier than the effort of going thro the rads
gotoPzero said:
I was wondering if the zone valve was not opening causing this "backup" and thus cycling of the boiler.
Its hard to tell as our hot water comes on at 6am, so I think to test it out I will have to move this to in the daytime to really see whats going on.
Actually that's may be a good possibility if it's not fully opening and thereby causing a restriction in the circuit that means too little flow thro the boiler then the temps would spikeIts hard to tell as our hot water comes on at 6am, so I think to test it out I will have to move this to in the daytime to really see whats going on.
gotoPzero said:
Regarding taking the zone valve off.... is this easy to do?
Most have removable actuator units (Drayton for sure does) but some don't gotoPzero said:
The boiler will fire up, run to about 40c and then shut down.
Like its not detecting any flow maybe?
It seems to do this 2-3 times in a row then shuts off all together.
Like its not detecting any flow maybe?
It seems to do this 2-3 times in a row then shuts off all together.
Edited by B'stard Child on Monday 3rd February 13:08
I have seen it do both I think it depends if its the first go from calling the hot water or if its already mid way through.
From what I have seen if you boost just the hot water the temp goes 70+. When it gets to about 72/3 it tends to shut off.
This does not take long, maybe 10 seconds.
Then it cycles a few times, and finally it will settle about 35-40c ish - from what I have seen.
I am letting it cool off right now, so I will go shortly and have a proper look.
But knowing my luck it will work fine.
Cheers for the advice
From what I have seen if you boost just the hot water the temp goes 70+. When it gets to about 72/3 it tends to shut off.
This does not take long, maybe 10 seconds.
Then it cycles a few times, and finally it will settle about 35-40c ish - from what I have seen.
I am letting it cool off right now, so I will go shortly and have a proper look.
But knowing my luck it will work fine.
Cheers for the advice
gotoPzero said:
I have seen it do both I think it depends if its the first go from calling the hot water or if its already mid way through.
Mid way thro circuit is already warm/hot - from cold different scenario - differential isn't going to be as big even with a cold (ish) tank of watergotoPzero said:
From what I have seen if you boost just the hot water the temp goes 70+. When it gets to about 72/3 it tends to shut off.
This does not take long, maybe 10 seconds.
That specific scenario to me feels like not enough flow to satisfy the boiler - hence overshootThis does not take long, maybe 10 seconds.
gotoPzero said:
Then it cycles a few times, and finally it will settle about 35-40c ish - from what I have seen.
gotoPzero said:
I am letting it cool off right now, so I will go shortly and have a proper look.
But knowing my luck it will work fine.
Cheers for the advice
Feels like 2 issues But knowing my luck it will work fine.
Cheers for the advice
1. from cold circuit the zone valve for HW is sticking and only when it's had a reasonable amount of heat does expansion allow the motor head to overcome the resistance
2. from warm circuit the zone valve stands a higher chance of overcoming the resistance.
If you can remove the actuator head then put a small adjustable on the flats of the valve shaft and see how stiff it is to operate?
If you do feel a bit of resistance It maybe that working the valve a few times will free it up for a while
For about 12mths this was my HW/CH selection process - in the red circle an adjustable spanner on a three port valve.......
Long story but house had an early 80's Sunvic wiring centre/relay set up and zone valve - the zone valve died and I replaced it with a drayton 3 port - however I could never get it to work with the original Sunvic
Looked similar to this
Ended up rewiring the whole thing to get it working properly
Long story but house had an early 80's Sunvic wiring centre/relay set up and zone valve - the zone valve died and I replaced it with a drayton 3 port - however I could never get it to work with the original Sunvic
Looked similar to this
Ended up rewiring the whole thing to get it working properly
Just ran a test.
Boiler @ 25c "cool" turned off.
Called for water
Boiler temp every 1 min
1 min 37
2 min 71
3 min 66
4 min 67
5 min 67
I was monitoring temp at the zone valve on each side and the valve opened as it should and temp was stable and reflected the boiler temp.
After 5 min I turned the water stat on the cyl down from 70 to 40.
The valve closed, and the boiler went into cool down mode.
1 min 63
2 min 63
3 min 63
4 min 63
5 min shutdown
I then called for water again, this time the boiler was obviously hot. Heat up was a bit different took 7 mins
1 min 54
2 min 52
3 min 53
4 min 54
5 min 55
6 min 66
7 min 67
I think it must idle for 5 mins and it throttled up at 5 mins to 67.
I guess next step is to check the outflow of the cyl to see the temp drop.
To me, that looks like normal operation.
So I can only assume that for some reason that the zone valve is not opening when this fault happens?
There isnt really any other thing it could be? Well maybe the tank stat but I would not have thought its a regular point of failure?
Boiler @ 25c "cool" turned off.
Called for water
Boiler temp every 1 min
1 min 37
2 min 71
3 min 66
4 min 67
5 min 67
I was monitoring temp at the zone valve on each side and the valve opened as it should and temp was stable and reflected the boiler temp.
After 5 min I turned the water stat on the cyl down from 70 to 40.
The valve closed, and the boiler went into cool down mode.
1 min 63
2 min 63
3 min 63
4 min 63
5 min shutdown
I then called for water again, this time the boiler was obviously hot. Heat up was a bit different took 7 mins
1 min 54
2 min 52
3 min 53
4 min 54
5 min 55
6 min 66
7 min 67
I think it must idle for 5 mins and it throttled up at 5 mins to 67.
I guess next step is to check the outflow of the cyl to see the temp drop.
To me, that looks like normal operation.
So I can only assume that for some reason that the zone valve is not opening when this fault happens?
There isnt really any other thing it could be? Well maybe the tank stat but I would not have thought its a regular point of failure?
Update..
No hot water this morning. So I think there are 2 problems.
First problem - I boosted the water - and nothing happened.
Boiler just sat there. The green light came on to signal that the hot water was called.
I gave it a few minutes but it just sat there.
So I turned the dial down on the tank and it only clicked (off) at about 30c.
I then turned it back up - and it clicked again. But boiler still sat there.
I pressed the reset button on the tank thermostat and the boiler fired up.
So problem 1 - faulty thermostat?
Second problem.
I watched the boiler like a hawk and it fired up - ran at about 35c for 3-4 mins.
Then throttled up - great. Hit 60,65...70..starts to throttle down.....71,71,72,73 then shut down.
Egg timer on screen.
I have the flow temp set to 67.
Its overshooting. It is throttling down but I think its a thermal protection?
It then cycled like this 3 times, each time only running for total of about 5 mins.
Throttle up, throttle down, over shoot and shutdown.
I opened the valve to the radiators / heating to give it more of a "buffer" so to speak and tried again.
This time it worked ok and ran up to 67c. It did not overshoot.
Obviously a lot more volume of water to cool it.
What do we think?
New thermostat?
And then maybe some sort of setting in the boiler to stop the over shoot?
In winter this is not going to be a problem so much as the hot water comes on with the heating but in summer when the heating is not on much if at all I think this might be a real problem.
No hot water this morning. So I think there are 2 problems.
First problem - I boosted the water - and nothing happened.
Boiler just sat there. The green light came on to signal that the hot water was called.
I gave it a few minutes but it just sat there.
So I turned the dial down on the tank and it only clicked (off) at about 30c.
I then turned it back up - and it clicked again. But boiler still sat there.
I pressed the reset button on the tank thermostat and the boiler fired up.
So problem 1 - faulty thermostat?
Second problem.
I watched the boiler like a hawk and it fired up - ran at about 35c for 3-4 mins.
Then throttled up - great. Hit 60,65...70..starts to throttle down.....71,71,72,73 then shut down.
Egg timer on screen.
I have the flow temp set to 67.
Its overshooting. It is throttling down but I think its a thermal protection?
It then cycled like this 3 times, each time only running for total of about 5 mins.
Throttle up, throttle down, over shoot and shutdown.
I opened the valve to the radiators / heating to give it more of a "buffer" so to speak and tried again.
This time it worked ok and ran up to 67c. It did not overshoot.
Obviously a lot more volume of water to cool it.
What do we think?
New thermostat?
And then maybe some sort of setting in the boiler to stop the over shoot?
In winter this is not going to be a problem so much as the hot water comes on with the heating but in summer when the heating is not on much if at all I think this might be a real problem.
Is the pump in the boiler or external?
What pump is it if external and what is it set to?
To get an overshoot and shut down it must be a lack of flow to keep the boiler happy - add in CH and the flow might be the same but there will be a lower return temp so the boiler doesn’t overshoot with it’s min output
What pump is it if external and what is it set to?
To get an overshoot and shut down it must be a lack of flow to keep the boiler happy - add in CH and the flow might be the same but there will be a lower return temp so the boiler doesn’t overshoot with it’s min output
gotoPzero said:
The pump is in the boiler.
The boiler does not know if its doing cyl or rads it just knows flow temp.
It seems a basic set up.
Its been in for about 5 years I think so the previous owners have either just put up with it or maybe they did not realise?
Are you absolutely sure there is no restriction in the HW circuit - gate valve with an anti tamper cap or knob removed?The boiler does not know if its doing cyl or rads it just knows flow temp.
It seems a basic set up.
Its been in for about 5 years I think so the previous owners have either just put up with it or maybe they did not realise?
You said the boiler is in the same place as the HW Tank?
outnumbered said:
It sounds mostly like a faulty zone valve or actuator to me. I've just changed the actuator on a Danfoss zone valve that was causing a similar symptom on our system. Running the old actuator disconnected from the valve, you could see it wasn't always fully opening.
I don't think it is though because today from stone cold pressing boost nothing happened.It wasn't until I reset the tank thermostat did the boiler fire up.
B'stard Child said:
gotoPzero said:
The pump is in the boiler.
The boiler does not know if its doing cyl or rads it just knows flow temp.
It seems a basic set up.
Its been in for about 5 years I think so the previous owners have either just put up with it or maybe they did not realise?
Are you absolutely sure there is no restriction in the HW circuit - gate valve with an anti tamper cap or knob removed?The boiler does not know if its doing cyl or rads it just knows flow temp.
It seems a basic set up.
Its been in for about 5 years I think so the previous owners have either just put up with it or maybe they did not realise?
You said the boiler is in the same place as the HW Tank?
gotoPzero said:
I don't think it is though because today from stone cold pressing boost nothing happened.
It wasn't until I reset the tank thermostat did the boiler fire up.
Pressing boost would cause the valve to try to operate once. If it failed to work, then resetting the tank stat would also cycle the valve, and maybe that time it worked ok.It wasn't until I reset the tank thermostat did the boiler fire up.
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