Sporadic Hot Water - Unvented indirect

[Snrgruffalo]

Good Afternoon all,

I am hopeful someone may be able to offer some guidance on the following.

In the home we have a gas boiler (serviced annually, October time) providing hot water to the CH system which is split into 3 zones (Honeywell 2-way valves) and it also heats the HW tank (Tribune 145L) in the attic using the internal coil via a 2-way Honeywell valve.

All has been fine, until a 2-3 weeks ago we noticed that the HW feed from the shower temperature was dropping off quickly, CH was fine.

My initial thoughts was the mixer and started to look into that.

I then remembered to check the non-mixer HW tap in the bathroom sink, and alas that was also low in temperature. (Water pressure is very good on shower or tap)

Next step I went to check voltages on the thermostat attached to the cylinder, All appeared to be fine and Power signal was being returned to the valve switch. I then checked the Honeywell valve switch and all voltage are correct.

With power on and off I tested the valve switch to ensure the lever moves correctly.

While I was undertaking all this and pondering over what it could be a few days past and then unexpectedly we would have HW again, this would last for a week and then all of a sudden it stopped again.

I wondered if there was an intermittent fault, so I replaced the thermostat on the cylinder even though I could not see any issues with the one installed.

Unfortunately the HW still did not improve, so then I wondered if the Honeywell valve may be sticky and how to check if that was working or not.

After re-probing voltages and playing around with the lever the following morning there was HW not sure how much or if it is just another period were it will be ok and then stop again.

I am not hearing any strange sounds or seeing any other signs for concern, and in all this the CH system is working and the water is being pumped around the home fairly well, so I think the pump is ok.

Just wandering if anyone has some ideas, I am curious on the Honeywell valve and if its at all possible it could occasionally stick and not open and then open? - What is a good way to test for this?

Is it possible there is some air lock that’s preventing the heated water from pumping through the cylinder? - If so whats the best way to verify this?

Keen to learn on all this as i find it intriguing.

Many thanks in advance.

attached some photos of the system.

 

[oz-plumber]

If you have a tempering valve on the system, I would check that.

I think you guy's call it a blending valve.

That's the valve that is on the outlet of the cylinder that has 3 pipes plumbed to it.
Hot - from cylinder. Cold from mains & hot water to taps.

 

[Snrgruffalo]

Thanks for the response...will look into this.

Meanwhile a little update.

I placed a Thermometer on the Output feed of the cylinder could to see what temperate it would get to and then compare that with the input feed, which gets hot.

Turns out when monitoring the temperature gets to around 25C.

While monitoring I noticed that I can hear some irregular hissing, which turned out to be the Automatic Air Vent on the input pipework of the coil.

Closer inspection showed there was water coming out, not a lot but definitely some.

I was wondering that if this would be enough to unbalance the system and prevent the hot water present on the input of the coil having enough pressure to flow through the cylinder and out, which may be why the pipe temperature on the output pipe of the coil is not getting hot?

After noticing the water present I have turned the HW section off.

This morning I decided to try and catch it leaking in the act!

Needless to say i didn't catch it but while looking around in more detail and removing some of the insulation foam, there has definitely been more water than I thought.

So i wiped it down, placed some clothes on suitable areas to use as protection along with guides.

Turned the HW on and the input pipes started to heat up. Nothing else happened.

After a couple of hours all seemed stable but i was not convinced HW was passing into the coil as the output feed was around 20C and not really climbing.

I then turned on the Central heating, after an hour i went back up to the tank and firstly noticed the output pipe was 17C and then on touching the cloths these were soaked. (I missed it!) Also the input pipe had significantly dropped temperature. Checked the Honeywell switch and that was still open, so its almost as if what ever happened it also cooled the pipe down? the rest of the CH is still scorchio on the pipework.

More confused than before but still wondering if the pressure of water on the output of the coil is dominating ?

It also appears if I want to change the Air Lock vent on the input to the coil I will have to drain the whole HW/CH system.

 

[Basher]

Assuming it's the one in your 3rd photo top right, I would screw down the plastic cap on the automatic air vent to stop it leaking, or close the valve below it. There's enough vertical pipe there to catch air for many weeks! I can't see that contributing to the erratic hot water, so suggest you keep looking.

The Honeywell valve is a candidate. You could remove the actuator box to check if the valve stem is stiff.

Everything there is to know about Honeywell valves is on this website (and on John Ward's, to which there is a link):

Honeywell Motorised Valve Faults - Free Heating Advice

Honeywell motorised valve faults Common Honeywell motorised valve types Honeywell make a large range of motorised valves used in domestic central heating systems. The most common by far are the 22mm 3-port, 5-wire, mid-position valve and the 22mm 2-port, 5-wire, zone valve. These 22mm valves...

freeheatingadvice.com

The other thing to say, that may not be obvious, is that the power to switch on the boiler (and probably pump) for heating hot water often comes from the motorised valve, so if the valve doesn't reach fully open, the switch in the actuator head is not operated and the water is not heated. A reason for the valve not opening fully may be electrical or mechanical, as per the website referenced above.

 

[Snrgruffalo]

Thanks for the response. I realise the picture of the pipework around the tank is not clear.

This is the area were i first saw the hissing with water, and then what appears to be the source of the sudden loss of water. (Just above the blue rag). I tied the the rag on after finding water around the area and within the foam insulation (not shown in image as i had removed the foam insulation) The rag became sodden, and the pipe dropped in temp as described earlier.

From looking around the internet i see that this is the air lock valve and is on the feed going into to coil of the cylinder. My understanding is that it is placed there to expel excess air and water should not come out of it. It's in pretty crappy condition and what appears to be the manual vent screw(socket) head on the side is pointing towards the cylinder so not able to get an eyeball on it to see the condition.

Thanks for the link on valves will take a look.

As for the Boiler, so far i have not seen any issues with the boiler being switched on and heating the pipe, whether that is in HW mode or CH mode or both at the same time. I have also followed the electrical path to look for any intermittent changes.

I have also tried locking the Valve in manual mode and then switching the CH on and the heat passes the valve. No success on the Tank heating up though.

I will as i am interested is take a close look at the Valve to see if its more obvious to see it working correctly.

Thanks again for the guidance.

 

[Basher]

OK thanks for the response.
I hadn't understood it was a different vent leaking - I just saw the other, and assumed it would have the screw plug in the top!
If your leaking one is missing the knob I guess you can't screw it down to stop the leak!!

Sorry I don't have any suggestions! If there is very poor flow through the coil I was thinking a motorised valve somewhere was to blame, but it sounds like that is not the case