Boiler Not Heating the Hot Water Properly

[WhyMyBoiler]

Thanks, that makes sense... I'll see how the hot water performs tomorrow and I'll update this thread accordingly...

 

[Johntheo5]

May have been asked, what temperature is the boiler running at, ie the target or setpoint temperature?.

 

[WhyMyBoiler]

May have been asked, what temperature is the boiler running at, ie the target or setpoint temperature?

I'm not entirely sure in as much as the boiler itself only has a dial that goes from Low to High (see photo) and doesn't specify any particular temperature... This is the setting I've had it on since the boiler was installed (set by the plumber who installed it) and previously it's worked without issue...

 

[Johntheo5]

That seems turned well up.
What size is the HW cylinder?
Next time the water is being heated, feel the pipe coming off the bottom of the coil (outlet) it should be quit hot but not roasting hot.
Even though the CH is fine just ensure ther is water in the F&E Tank.

 

[WhyMyBoiler]

What size is the HW cylinder?

It's 900 x 450 (36" x 18") so 120 litres...

I'll check the pipe coming off the bottom of the coil (outlet) in the morning when the boiler kicks in, previously it has certainly been 'hot'...

Just checked the F&E tank and there is indeed water in there...

 

[WhyMyBoiler]

Just reporting back to say that opening the air vent on the inlet pipe made no difference...

The pipe coming off the bottom of the coil (outlet) is indeed very hot, i.e. the one shown in red in the photo but when drawing hot water by turning the hot water tap on the pipe that comes out of the top of the cylinder is hottish but not as hot as it should be...

I would describe the problem as being identical to this post, though it doesn't look as though the user reported back the actual cause...

Lukewarm water from cylinder

Hi I've got a problem with a cylinder (below) that only seems to produce lukewarm water : The water pipe going into the cylinder from the boiler system (shown below) is red hot when the hot water is switched on : But the pipe at the top of the cylinder is only lukewarm to...

www.diynot.com

 

[terryplumb]

Is the other pipe ( mid way up) that connects to the coil also as hot as the lower Pipe from coil ?

 

[WhyMyBoiler]

Is the other pipe ( mid way up) that connects to the coil also as hot as the lower Pipe from coil ?

Yes, they both seem to be as hot as each other I would say...

 

[Johntheo5]

I would expect a minimum of 10C difference, if the circ flow was say 15LPM then the coil output is 10.5kw so would take 40 minutes to heat your cylinder from a dead cold of say 10C to 60C. If there is air still present in the coill then one might expect the coil outlet to be cool, you could always, wih care, just slacken the top coil compression nut 3/4 of a turn at the cylinder and pull back the pipe to release any air, if present.
I know you had plenty HW after 20 minutes but maybe extend the heat up period to 45 minutes, even temporarily, it wont consume any more gas as the energy required to heat 120L from 10C to 60C is 7kwh, in practice, the cylinder will probably be ~ 25C so energy required ~ 6kwh allowing a boiler efficiency of 80%.

 

[WhyMyBoiler]

I would expect a minimum of 10C difference

It could well be, I simply did a hand touch to feel how hot both pipes were...

You could always, with care, just slacken the top coil compression nut 3/4 of a turn at the cylinder and pull back the pipe to release any air, if present.

I assume you mean this one? I also assume I would do that when the boiler is not running is that correct? If I try that would I expect to hear a release of air if there is any trapped or for any water to seep out?

Once done, then obviously I would tighten it back up again to how it is currently... (sorry for the dumb questions again)...

Thanks for the advice, I will also run the boiler for an extended time (45 minutes) to see if that improves things and report back.

 

[Johntheo5]

NO, don't touch that, I'm talking about the pipe from the boiler that enters the coil (top coil connection), if you'r not sure don't touch it, just run it for 45 minutes or so.

 

[WhyMyBoiler]

Thanks for clarifying... will just run for 45 mins and see if that changes anything... many thanks

 

[WhyMyBoiler]

Just providing an update to this thread...

Having tried everything suggested above, apart from slackening the top coil compression nut 3/4 of a turn at the cylinder and pulling it back the pipe to release any air, if present I still have the same issue.

I decided to check the hot water temperature coming out of the taps this morning using a kitchen thermometer at it's only 45 degrees.

So despite the pipe with the two connections to the hot water cylinder and the air vent at the top being red hot to the touch when the boiler is running (I've not checked the temperature of that pipe yet) and the temperature on the hot water cylinder being set to 65 degrees, the water coming out of the hot water taps is 20 degrees lower.

Based on that would this still potentially suggest an airlock in the hot water cylinder since the pipe leading from the top of the hot water cylinder is hot but not red hot when the hot water taps are on and if so would draining the entire system and refilling it potentially clear any airlock?

Or

Could there potentially be a fault with the coil in the hot water cylinder and if so, how would you check?

Or

Is there any likelihood that the issue could be with the boiler itself? The fact that the radiators are red hot to the touch when on suggests not but I'm still trying to figure out possible causes and remedies.

Many thanks to all who've taken the time to respond, it is very much appreciated.

 

[Johntheo5]

Just providing an update to this thread...

Having tried everything suggested above, apart from slackening the top coil compression nut 3/4 of a turn at the cylinder and pulling it back the pipe to release any air, if present I still have the same issue.

I decided to check the hot water temperature coming out of the taps this morning using a kitchen thermometer at it's only 45 degrees.

So despite the pipe with the two connections to the hot water cylinder and the air vent at the top being red hot to the touch when the boiler is running (I've not checked the temperature of that pipe yet) and the temperature on the hot water cylinder being set to 65 degrees, the water coming out of the hot water taps is 20 degrees lower.

Based on that would this still potentially suggest an airlock in the hot water cylinder since the pipe leading from the top of the hot water cylinder is hot but not red hot when the hot water taps are on and if so would draining the entire system and refilling it potentially clear any airlock?

Or

Could there potentially be a fault with the coil in the hot water cylinder and if so, how would you check?

Or

Is there any likelihood that the issue could be with the boiler itself? The fact that the radiators are red hot to the touch when on suggests not but I'm still trying to figure out possible causes and remedies.

Many thanks to all who've taken the time to respond, it is very much appreciated.

You have run it for 45 minutes?

Check the boiler flow (outlet) temperature.

You will have a motorized (zone) valve which stays open once HW is selected on and the cylinder stat is calling for water, you will either have seperate valves for the CH and HW or just one, called a mid position valve, with three pipes, try and locate these/this.
I cant see the cylinder stat scale clearly, what is it?, and what setting is it on?, turn the dial slowly anticlockwise (until you hear a click, note the reading, turn it back up slowly until you hear another click and note this, return it to its original setting.

 

[WhyMyBoiler]

You have run it for 45 minutes?

I did and yes, that resulted in 'proper' hot water the following day, but since then I've had it back on 20 minutes to see what real difference it's made and it's slowly reverted back to lukewarm water.

In the ten years I've had this boiler I've never once had to run it for 45 minutes to get piping hot water at the correct temperature.

Check the boiler flow (outlet) temperature.

I'll do that in the morning when the boiler kicks in again.

You will have a motorized (zone) valve which stays open once HW is selected on and the cylinder stat is calling for water, you will either have seperate valves for the CH and HW or just one, called a mid position valve, with three pipes, try and locate these/this.

I assume you mean the 3-position diverter valve? This was replaced quite recently as it was faulty but is there anything I should check that could indicate whether it's become faulty again?

I cant see the cylinder stat scale clearly, what is it?, and what setting is it on?

It's a Honeywell L641A1039 Cylinder 230 V Stat and it's currently set to 65 degrees.

I cant see the cylinder stat scale clearly, what is it?, and what setting is it on?, turn the dial slowly anticlockwise (until you hear a click, note the reading, turn it back up slowly until you hear another click and note this, return it to its original setting.

I only seem to hear a single click when the dial is turned to approx 38 degrees or possibly if there are two clicks is within a range of about 35 to 38 degrees I would say.

Normal Setting - Left | When I Hear a Click - Right

Boiler Layout (In case it helps)

The 3-position Diverter Valve From the Top and Bottom