Heating fine but water only luke warm

MuddyDog

Hi.

Have a boiler in the garage, hot water cylinder in the hotpress upstairs and a water tank in the attic.

3 pics attached of the system. Basically the water started to only become luke warm recently and since last night it now just doesn't heat at all (always cold). I have 2 diverter valves that are relatively new on the sytem as can be seen in the pics. When I use my Hive and turn on just the hot water, then the boiler fires up and the Flow pipe into the tank is too hot to touch coming from the boiler but if I touch the pipe that enters the actual cylinder, it's hot, but bearable to touch. Strangely after 10 mins-ish each time (from cold) the boiler shuts off as if the cylinder is saying I'm at temperature (thermo on cylinder is 65 degrees). I've checked the thermostat and it's working fine and is always live telling the boiler to be on so I'm guessing the boiler thermo is shutting it down. The coil return pipe is always stone cold as is the pipe coming out the top of the tank which runs to our hot taps. Would a blockage inside the cylinder prevent the flow of water and therefore the boiler would get too hot and shut down itself or could it be caused by an airlock?

There is a pressure gauge in the picture too which was at 0 when we first went into the hotpress to try and diagnose the problem so I assume this is something to do with it all? Usually it would sit between 1 and 2 bar. I opened the valve just above the gauge to let water in to increase the pressure (as we normally have to do this every few months for whatever reason) but on this occasion it wouldn't budge and remained at 0. So then, we pumped air into the red expansion tank in the cylinder and this got the pressure gauge right up to 2 bar again. However, it's been the same issue since!

A long old post there so appreciate you taking the time to read it. Any ideas at all?

John.G

Gas or oil boiler?
one or two expansion vessels?
Is the cylinder vented or unvented, ie fed from the cold water storage tank or fed from the mains.?
Cylinder "Coil Flow" has nothing connected to it.
You increased the air end pressure to get the water side pressure up, I would bleed off air until pressure reads 0 again, you may have a pumped system so open a tap somewhere to start the pump ans see can you top up the E.vessel (water side), before doing this ensure you have 1 bar at air side then top up with water until PG reads 2 bar.
You probably have a motorised valve on the flow pipe to the cylinder coil, ensure this is opening when cylinder stat calls for heat.

Wearb

Sounds like your automatic fill valve is stuck. Your expansion vessel is most likely at wrong pressure now after pumping it.

John.G

It was increased (incorrectly) by increasing the air pressure so should have started heating again but with the very likely prospect of lifting the boiler PRV when system. heated up.

MuddyDog

John.G wrote: »

Gas or oil boiler?
one or two expansion vessels?
Is the cylinder vented or unvented, ie fed from the cold water storage tank or fed from the mains.?
Cylinder "Coil Flow" has nothing connected to it.
You increased the air end pressure to get the water side pressure up, I would bleed off air until pressure reads 0 again, you may have a pumped system so open a tap somewhere to start the pump ans see can you top up the E.vessel (water side) before doing this ensure you have 1 bar at air side then top up with water until PG reads 2 bar.
You probably have a motorised valve on the flow pipe to the cylinder coil, ensure this is opening when cylinder stat calls for heat.

Oil boiler.
There is 1 expansion vessel connected to the cylinder as per pics. However in the attic connected to the Water Tank there are 2 more expansion vessels.
The cylinder is fed from the tank in the attic I'm nearly positive as the inlet pipe at the very bottom of the cylinder goes straight up to the attic where the tank is. It is a pumped system as there is indeed a pump in the attic.

How do I bleed the air off so it reads 0 again? Basically just press down on the expansion vessel valve in the pic so I hear air coming out?

Yeah it is opening when calling for heat (the diverter)

John.G

Yes, bleed air off via that valve, then get the pump to start by opening a tap somewhere and let it open until you re pressurize the system.

If your HW cylinder is vented, then you will see a open ended pipe bent over the top of the cold water storage tank.

MuddyDog

John.G wrote: »

Yes, bleed air off via that valve, then get the pump to start by opening a tap somewhere and let it open until you re pressurize the system.

If your HW cylinder is vented, then you will see a open ended pipe bent over the top of the cold water storage tank.

So I reduced the air pressure by pressing down the valve on the Expansion vessel. However the gauge wouldnt go lower than about 1 bar. So then I ran a tap and opened the valve above the pressure gauge but that only topped it up to maybe 1.5 bar. It's worth noting that usually I would open that valve without a tap running and the pressure gauge would increase. It just doesn't increase now no matter what when trying to open the water valve. There is a black valve actually on the PG itself but don't think that should need altering considering the system worked fine previously?

I turned the hot water on anyways when I got the pressure up to 1.5 bar and again, boiler came on for about 10 mins before shutting off. Pipe entering the cylinder again was hot but I could touch it fine but then boiler went off.

Attached pic of the top of my cylinder so you can check if it's vented or not?

John.G

There is a item with a green label up near the cylinder top, if that is reading 6 bar or mavbe 7 bar then you have a unvented HW cylinder. Also which E.vessel are you reducing the air end pressure on??

MuddyDog

John.G wrote: »

There is a item with a green label up near the cylinder top, if that is reading 6 bar or mavbe 7 bar then you have a unvented HW cylinder. Also which E.vessel are you reducing the air end pressure on??

Yeah the green sticker says 7 bar. So unvented means the cold water is fed into the cylinder from the mains right? How come the inlet pipe leads straight up to the attic? Should I try and trace that pipe to see if it actually is attached to the tank in the attic?

I reduced the air pressure on the red expansion vessel in the pics. The other E. Vessels are all in the attic.

John.G

That red E.vessel is IMO for the HW cylinder and has nothing to do with the heating system, it may or may not be fed from the mains but if you have a fairly hefty looking pump that cuts in/out regularly then that pump takes water from the cold water storage tank and pressurises it to supply both the cold and hot water. You really should get a qualified person to recharge that E.vessel but IF that pressure gauge is associated with it, then when you do eventually get the HW cylinder heated up, as long as the pressure doesn't rise higher than 3 or 4 bar you will be OK, if it starts rising further then turn off the the cylinder heating and get someone in.
Can you take as many photos as possible of the E.vessels and pressure gauges in the attic and also see if one connects in to the HW cylinder heating coil.
Have you got a solar system as well.? Will be back in ~ 2 hrs or so.

MuddyDog

Appreciate the help John. Will take those pics of the attic now for you. Yeah we have a decent pump in the attic which I'll also take a pic of. That PG I believe is an automatic fill valve (looks like this exact one https://www.topline.ie/plumbing-heating/plumbing/pipe-fittings/valves/biworld/automatic-filling-valve)
No solar system installed.

John.G

Not gone yet, that PG is connected to a pressure reducing valve (also called a PRV) follow this pipe downwards and see if its connected to the HW cylinder coil flow or return pipes or is connected to where the cold water enters the cylinder. Also see where the pipe from that red E.vessel joins the system to confirm that it is the E.vessel associated with the HW cylinder.

MuddyDog

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Pics from the attic and 1 more of the cylinder. The pic of the cylinder is https://ibb.co/rQqWMjC
From this pic my finger is touching the pipe connected to the red E.Vessel. You can see there is then a join on it. That join runs to the Coil Return. Continuing on you see it goes down and turns left before we meet another join. That join goes up to the pressure gauge and above the pressure gauge you see the tap valve.

MuddyDog

Coupel of different angles of the pressure gauge as well so you can maybe see better what's going on. I've labelled them as well too. The red cross on each pic is the pipe connected to the red E.Vessel. The pipe that is connected above the HW diverter is the coil flow pipe that goes into the cylinder.


I noticed as well when up in the attic that the pressure and temp relief valve up at the top of the cylinder (the 7 bar green sticker knob) goes straight back up into the water tank in the attic. I thought this was meant to go downwards so that if you needed to open it you'd be able to get water OUT of the system rather than putting it up into the tank?

John.G

That red vessel does seem to be the E.vessel for the boiler system expansion so any pressure > 1.5 bar should be fine, normally, with a depressurized system the E.vessel would have a pre charge (air end) pressure of 1 bar and the filling (water side) pressure 1.5 bar with a cold system, on heat up the pressure might then increase to ~ 2/2.3 bar.

Is the CH side of things OK and heating up normally.
You might check the capacity of that red E.vessel.
Also the capacities of the two blue E.vessels in the attic and where they are attached.
The HW cylinder itself should have a E.vessel of ~ 18 litres or more so wonder where the expansion is being accommodated.

If the CH (rads) side of things is OK then difficult to see why no circulation through the cylinder coil, perhaps air or sludge if the system is very dirty.
If the boiler circ pump is external can you post the make/model and setting.

The T&P PRV waste pipe should terminate into a tundish and then to drain.

MuddyDog

Also should note the actual immersion heater in the cylinder isn't working either!? It'll be on for an hour and only cold water from the taps.

MuddyDog

.

John.G

If the 3kw immersion is located in the bottom of say a 250 litre cylinder, then in 1 hour it will only increase the water temperature by ~ 10C, if located in the bottom, leave it on for 3 hours and then you should get hot water.
Also feel the pipe right at the top of the cylinder just in case that there is some downstream mixing of cold and hot water.

MuddyDog

Ok will leave it on for a long time. Is it possible that the coils inside the cylinder are blocked with sludge and therefore the hot water cannot pass thru a certain point anymore meaning the boiler therefore heats up really fast and trips off? This seems to me what's happening because the boiler will run for a few mins then shut down for a while then start up again for a few mins.

Pipe right at the top of the cylinder is stone cold. As in the coil return.

John.G

Yes, if very poor circulation the boiler will cycle very rapidly bearing in mind that a oil boiler will always cycle since it operates at full output all the time.

Any idea of the pump make/model and setting?. and does the CH operate OK?.
I would also be inclined to remove the actuator from the cylinder motorised valve and see if the valve is opening closing OK.

MuddyDog

CH is fine.

Removing the actuator from the cylinder motorised valve? Which valve (HW or CH) and by remove do you just mean slide the lever manually over to Flush mode?

Will try and get make model of the pump.

John.G

Off the HW, by removing a few screws you should be able to lift it right up and off the valve spindle.

MuddyDog

Will try that tomorrow....but the fact that the pipes are getting pretty hot entering the cylinder must mean the valve is open and allowing hot water to pass through? So why do you think the valve could be an issue?

John.G

Fair enough then if you are happy enough based on the pipe work temperatures, what you might consider is ensure the motorised valve closed then slacken the compression fitting where the (flow) pipe enters the cylinder and pull back the pipe a touch to see if any air then water comes out, otherwise you may have to drain down the whole system to check sludge/blockage in the coil.

MuddyDog

Thanks. Likely I will have to drain. Is it enough to just drain the cylinder while gating off all the pipes that flow into it and then checking the flow coil and return for air and dirt or do I have to turn off the main water and drain the entire house essentially?

John.G

I would just try and drain the coil to see its condition.

MuddyDog

Drained the coil. Plenty of air and a couple of litres of water came out so thought I might be onto a winner. When I did this the pressure went to 0 on the gauge. No blockage it seems in the coils anyway. Put it all back together and turned on the tap above the pressure gauge and heard water rushing in and the pressure gauge got up to 2 and then I turned it off. Turned on the HW and the pipe entering the cylinder got roasting hot...couldn't touch it and previously I could. However the return is still cold an hour later and the water is just luke warm still. The boiler cuts out too soon I think and then the pipes cool a lot before firing up again. Something still isn't right!

K.Flyer

Sorry if asked already, but is the cylinder coil balancing valve opened enough, have you tried opening it fully?

MuddyDog

Not sure what the balancing valve is?! Is it the little pipe that connects the flow from the boiler to the return pipe out of the cylinder as can be seen in the pic called pipes1 a few posts back?

K.Flyer

On the coil return is there a red round handled valve similar to the rest of them. Check the full length of the pipe.
Also, is that small chrome valve connecting between the coil flow and return?
Is it fully open or closed or partially open?

MuddyDog

Is this it circled in red? The orange pipe is the flow from boiler. Yellow is the coil flow to the cylinder. Blue is the coil return from the cylinder.