Where's my hot water?

Hurrache

I've a Viessmann Vitodens 100 condenser boiler, installed 2 years ago, two zones, heating and water, controlled by a Nest and there's a thermostat on the boiler in the hotpress.

Hot water availability seems to be patchy, I initially put it down to the drop in temperatures last week but I think it may not be heating it at all now.

This morning there wasn't much hot water, and what was there was luke warm at best. I put it back on and it gave us enough hot water for showers then, it was pretty hot. Later this evening there was no hot water again, despite it being on during its usual schedule, a half hour.

So again I put it on. The gas boiler switches on when the nest calls it and I can hear the whirring of valves opening in the hotpress. But the water doesn't seem to be getting hot.

The radiators when the heating is on are hot so no issues with the heating. The LCD display on the gas boiler showing the temperature in the system fluctuates wildly when on, showing a range of about 20c in the space of a minute or two, don't know if that's normal behaviour.

Any ideas? Could it be the thermostat on the water boiler in the hotpress sending back dodgy readings to the gas boiler indicating it's warm enough? When the heating is on we get this annoying ticking via the pipes so not sure if that's relevant.

amecullen

Hi
I am having exactly the same problem, would really appreciate any insights?

John.G

Hurrache wrote: »

I've a Viessmann Vitodens 100 condenser boiler, installed 2 years ago, two zones, heating and water, controlled by a Nest and there's a thermostat on the boiler in the hotpress.

Hot water availability seems to be patchy, I initially put it down to the drop in temperatures last week but I think it may not be heating it at all now.

This morning there wasn't much hot water, and what was there was luke warm at best. I put it back on and it gave us enough hot water for showers then, it was pretty hot. Later this evening there was no hot water again, despite it being on during its usual schedule, a half hour.

So again I put it on. The gas boiler switches on when the nest calls it and I can hear the whirring of valves opening in the hotpress. But the water doesn't seem to be getting hot.

The radiators when the heating is on are hot so no issues with the heating. The LCD display on the gas boiler showing the temperature in the system fluctuates wildly when on, showing a range of about 20c in the space of a minute or two, don't know if that's normal behaviour.

Any ideas? Could it be the thermostat on the water boiler in the hotpress sending back dodgy readings to the gas boiler indicating it's warm enough? When the heating is on we get this annoying ticking via the pipes so not sure if that's relevant.

The cylinder thermostat normally opens a motorized valve on the cylinder coil which allows hot water to circulate through the coil, the valve (contacts) also sends a signal back to the boiler to start up. Check and see if this valve is actually opening, you can do this by turning the temperature control on the thermostat down to minimum and then back up to max, it is normally set at 60C. There may also be a balancing valve fitted on the coil outlet, open this fully, then close it and reopen it about one to one and a half turns. (normally about 4 to 5 full turns between fully open/closed).

Hurrache

Cheers for that John, the issue turned out to be something a bit more mundane for us anyway.

amecullen, I figured it coincided with 2 things. First was a drop in temperature and therefore the water temperature. We don't have an outside temperature sensor fitted to I manually increased the temperature at the boiler.

Secondly was a change in our routine as to when we turned on our dishwasher, we had reduced levels of hot water after a run. So I checked the plumbing and saw that it was fitted to run off the hot tap, instead of the cold tap. Don't know why the fitter done it that way as I checked the manual and it can be ran off either hot or cold. Next time I have a plumber around I'll get them to replumb it as I don't think there's a spare cold connection for me to do it myself (I suspect that is indeed why the fitter plumbed it off the hot water).

Passrby

Hi all,
I am having a problem with hot water from my back boiler.

I bought a house and as part of the refurb I got an insert stanley stove with back boiler installed.

When I light the fire, all the rads in the house get very very hot but even after hours of the fire lighting I have no hot water, only luke warm water.

When I switch on the emersion however I get plenty of hot water so it just seems like back boiler only heats the rads.

What could be causing this, my parents have a stanley and they have boiling hot water from the stove so I dont know what is diferent with my own.

Any opinions??

Thanks,
Thomas

shane b

My sister rents a cottage with a back boiler stove. There is an adjustable thermostat attached one of the pipes close to the circulating pump. This stat turns the circulating pump on or off depending on the water temperature. If she turns the stat low around 30 it starts the pump sending most of the water to the rads. If she sets it to say 70 the pumps off until the water gets hot and the cylinder water is heated first. She uses the electric shower in the house most of the time so her need for hot water isn't massive.
Don't know if your heating is set up similar but it may be worth checking out.

amecullen

Thanks for the advice,
Checked the stat on the cylinder- all ok.
Had the boiler serviced recently, our water was super hot up until then.
The guy said he “rebalanced” the system would that have any effect on the temperature of the hot water?
Also he reset the temperature on the boiler to the recommended setting it had been higher.
So we now heat the water for two hours at the recommended setting and it is Luke warm.
Previously we heated the water for one hour at a higher boiler temperature and had lots of very hot water.
Which is the most efficient/cheapest way to get hot water, should I increase the number of hours or increase the boiler temperature?

Wearb

amecullen wrote: »

Thanks for the advice,
Checked the stat on the cylinder- all ok.
Had the boiler serviced recently, our water was super hot up until then.
The guy said he “rebalanced” the system would that have any effect on the temperature of the hot water?
Also he reset the temperature on the boiler to the recommended setting it had been higher.
So we now heat the water for two hours at the recommended setting and it is Luke warm.
Previously we heated the water for one hour at a higher boiler temperature and had lots of very hot water.
Which is the most efficient/cheapest way to get hot water, should I increase the number of hours or increase the boiler temperature?

Probably neither. It might be that he turned down the cylinder coil valve too much. Post a pic of the cylinder with the coil input/output pipework.

John.G

amecullen wrote: »

Thanks for the advice,
Checked the stat on the cylinder- all ok.
Had the boiler serviced recently, our water was super hot up until then.
The guy said he “rebalanced” the system would that have any effect on the temperature of the hot water?
Also he reset the temperature on the boiler to the recommended setting it had been higher.
So we now heat the water for two hours at the recommended setting and it is Luke warm.
Previously we heated the water for one hour at a higher boiler temperature and had lots of very hot water.
Which is the most efficient/cheapest way to get hot water, should I increase the number of hours or increase the boiler temperature?

The boiler temperature has a big effect on the heat/reheat time of the hot water cylinder. Some boilers increase it automatically from say 50/55C to 70/80C with hot water zone calling for heat. The circulating flow rate through the coil also has a effect. Because both may have been adjusted by your plumber then I would advise a boiler set point of 70/75C and to quote from my own #3 post above "There may also be a balancing valve fitted on the coil outlet, open this fully, then close it and reopen it about one to one and a half turns. (normally about 4 to 5 full turns between fully open/closed)."

My own 100 litre hot water cylinder takes 65 minutes to heat from 15C to 55C and 35 minutes to reheat from 40C to 55C. with (oil fired) boiler average temperature of 70C.

amecullen

Are these images ok?

amecullen

John G. Thanks for that information, my Vitodens 100-W WB1B compact condensing boiler boiler temperature is set to 5. When the boiler is on it climbs to a reading of 55 then quickly falls to 28 then starts climbing back up 55 then same again. So should I move the setting up ? Will this effect the efficiency of the heating? All our rads are currently heating up well.

I have uploaded pictures of the cylinder. Is this the valve ?

John.G

amecullen wrote: »

John G. Thanks for that information, my Vitodens 100-W WB1B compact condensing boiler boiler temperature is set to 5. When the boiler is on it climbs to a reading of 55 then quickly falls to 28 then starts climbing back up 55 then same again. So should I move the setting up ? Will this effect the efficiency of the heating? All our rads are currently heating up well.

I have uploaded pictures of the cylinder. Is this the valve ?

Yes......the cylinder balancing valve is that (red) one on the coil outlet. If the cylinder stat is mounted where it appears to be (high up on the left of picture) then its in the wrong place, it should be mounted ~ 1/3rd of distance between the coil flow & return pipes so that the motorized valve is energized open when only a small volume of water has been drawn off. If the thermostat is located properly then check that the motorized valve which should be mounted on the coil (top) flow pipe is opening fully.

There is a huge differential of (55-28) 27C which certainly isn,t normal, it should only be 10C to 15C at the most as the above is only giving you ~ a average boiler flow temperature of 41.5C which won't heat much, you might recheck those readings before changing anything as you may have a boiler problem.
Edit: Also check that differential when the rads are calling for heat to see if its any different as you may only have a very small flow through the coil. You can check that coil balancing valve "now".

amecullen

Hi Guys

That has been hugely helpful. I checked the boiler temperature with just the heating. It stayed at between 53-55. I put the heating and the hot water on and it stayed the same.

So the differential is only a problem with the hot water on its own.

We had a problem with our cylinder thermostat. It is a sunvic SA 2452/ receiver TLX 1206. When the batteries failed this time (I have replaced them successfully before) the units would not synch. The guy who serviced the boiler, put the receiver into manual mode.

But looking at this now, the receiver has a yellow light ON a red light ON and the green light is BLINKING continuously. I now suspect this is the problem.

He suggested replacing all our sunvic controls with an EPH system, but he hasn’t come back to me yet with a price and seemed to be put off by the fact that we would not get a grant to replace the controls.

It looks like this may explain why we had variable hot water, we get hot water when we run the two together and Luke warm water when we run the water on it’s own (still looking into this)?

I know we need to replace our cylinder thermostat but our Sunvic system is in place 10 years and I am considering replacing it with a better one, I would prefer a system that is easier to manage, I am neither a plumber nor an electrician.

Nest maybe? (But I don’t think this comes with a cylinder thermostat)
Does a cylinder thermostat make much of a difference?

Need to decide the best way forward. Any advice much appreciated

John.G

amecullen wrote: »

Hi Guys

That has been hugely helpful. I checked the boiler temperature with just the heating. It stayed at between 53-55. I put the heating and the hot water on and it stayed the same.

So the differential is only a problem with the hot water on its own.

We had a problem with our cylinder thermostat. It is a sunvic SA 2452/ receiver TLX 1206. When the batteries failed this time (I have replaced them successfully before) the units would not synch. The guy who serviced the boiler, put the receiver into manual mode.

But looking at this now, the receiver has a yellow light ON a red light ON and the green light is BLINKING continuously. I now suspect this is the problem.



He suggested replacing all our sunvic controls with an EPH system, but he hasn’t come back to me yet with a price and seemed to be put off by the fact that we would not get a grant to replace the controls.

It looks like this may explain why we had variable hot water, we get hot water when we run the two together and Luke warm water when we run the water on it’s own (still looking into this)?

I know we need to replace our cylinder thermostat but our Sunvic system is in place 10 years and I am considering replacing it with a better one, I would prefer a system that is easier to manage, I am neither a plumber nor an electrician.

Nest maybe? (But I don’t think this comes with a cylinder thermostat)
Does a cylinder thermostat make much of a difference?

Need to decide the best way forward. Any advice much appreciated

I'm afraid not familiar with these systems but it may just be possible to replace the (sunvic) cylinder stat with a conventional one depending on what you find below.
A cylinder thermostat is essential in a system that can be selected to hot water only, in systems which have separate motorized valves when hot water only is selected the live supply in series with the programmer and the cylinder stat will direct the motorized valve on the cylinder coil to open, a separate switched supply in this motorized valve will then fire up the boiler which will continue to fire (cycle on/off) until either the cylinder stat is satisfied (cyl up to temperature) or the programmer times out or is switched out.
You might have a look and see what the motorized vave looks like on the hot water cylinder, ie is it a 2 way valve (pipe in and out) of if you have a motorized valve mounted somewhere else (3 way) with 1 supply pipe in and 2 out, 1 each to the central heating and hot water cylinder coil.
Also do you have two separate sunvic transmitters, one to select CW or HW or both CW&HW and a separate transmitter for the cylinder thermostat.

amecullen

Hi
Still troubleshooting this problem.
I have two motorized valves in the kitchen beside the boiler.
One is marked hot water and a red light comes on this when the timer requests hot water. The red light on the other one comes on when the timer requests heating. There is one pipe in and out of these so I assume this means they are 2 way.
There are two separate RF transmitters, one from the other I presume is from the RF room thermostat. Neither of these are working at the moment.

The guy who did the service is a registered RGII engineer. But I have no faith in him now.
I think I need a professional heating engineeer who understands these systems to review the system and advise us. I would appreciate any recommendations by PM. I am based on the south side of Dublin, just off the M50.

amecullen

An update

I had another engineer look at this.
He changed the service setting on one of the dials on the boiler. Apparently the first engineer left it in the wrong position.
Hey presto, everything working as it should, lots of hot water.
Lesson learned, I’ll not be using the RGII registered and Viessmann trainee/approved engineer any more.
Thanks very much for all your advice and help troubleshooting this.

zl1whqvjs75cdy

amecullen wrote: »

An update

I had another engineer look at this.
He changed the service setting on one of the dials on the boiler. Apparently the first engineer left it in the wrong position.
Hey presto, everything working as it should, lots of hot water.
Lesson learned, I’ll not be using the RGII registered and Viessmann trainee/approved engineer any more.
Thanks very much for all your advice and help troubleshooting this.

Would you mind pming me his name please. Looking for a competent engineer to have a look at my system.