Potterton Megaflow system - no hot water

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Hi, hoping for some help please.

We have an unvented system with Megaflow cylinder, but not getting hot water from the boiler. Heating working fine.

We had an engineer out who replaced the diaphragm and then the pcb, but still nothing. He suggested the motorised valve next, but I have no faith in him.

I’ve had a look through guides and it may point to this. When I turn on the heating one valve opens and the boiler fires with no issues.

When I try to turn on the hot water there’s no movement in the second valve. I can open it manually using the valve lever and the water flows through, so no blockage at least.

So, how do I work out if it’s a fault in the tank stat, valve head, the Hive programmer, or something else?

I appreciate your help.
 
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Was it working before or is the hive a new addition ? if it did work before I think you are correct and its most likely to be the HW zone valve, but you will need multimeter to test to make sure, I would ditch your engineer , why on earth he thought it was the pcb when you have heating, as you said you can slide the lever across on the zone valve, you can lock it in that position as a temp move and if the heating is on it will heat the tank for you, but will only work when the heating is on untill you get it sorted
 
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Hi Ian, thanks for the reply.

We had Hive installed 4/5 years ago, this is a new issue.

I'll look out a "how to" for testing the zone valve and get the head replaced if that turns out to be the issue.

PCB may be my fault. I said to him that it had been replaced a couple of times already, so he would have had that in his mind most likely.

Thanks again!
 
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I can open it manually using the valve lever and the water flows through, so no blockage at least.
How do you know the water flows? Is the pump running in that situation? Is the boiler firing?
as you said you can slide the lever across on the zone valve, you can lock it in that position
Does the valve microswitch still close when the valve is opened manually? Just asking, I don't know, though I'd guess it would. If so that allows water heating as a stopgap, but obviously it ignores the water temp so need to close the valve when it's hot enough.
 
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Does the valve microswitch still close when the valve is opened manually? Just asking, I don't know, though I'd guess it would. If so that allows water heating as a stopgap, but obviously it ignores the water temp so need to close the valve when it's hot enough.
no it wont make the end switch as the manual lever is intended for use when you are filling the system, but the CH valve is working so if the heating is on that will send power to boiler to fire
 
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no it wont make the end switch as the manual lever is intended for use when you are filling the system, but the CH valve is working so if the heating is on that will send power to boiler to fire
OK thanks. So for the flow OP described, CH must have been calling.
 
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OK thanks. So for the flow OP described, CH must have been calling.
yes, sometimes on the honeywell ones if you move the lever open fast you can hear the micr0 switch making for a second or so and if nothing else on you will hear the pump coming on briefly
 
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Thanks for the replies.

I opened the hot water valve manually when heating was calling, so know there’s no blockage in the valve as water flowed.

I have ordered a replacement head and will change at the weekend when I have a chance, so hopefully that will resolve the issue. I’ll post back once done to confirm
 
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Replacement head received and fitted this evening. Fault remains :mad:
Could it be that the central heating valve needs replaced? I've just replaced the hot water valve.
Anything else obvious I should be checking?
 
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Could be the over heat stat on the cylinder tripped. Depending on what type of cylinder thermostat you have some have a little red button you press to reset them. Post a picture of it if you can't figure out to reset it and we can help you
 
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Thanks for the reply johnmdc

I’ve pressed the reset button on the stat and will see if that’s fixed it. There was no obvious click, just feels dead when I press, but that may be normal?

I didn’t say before, but the electric element on my Megaflo cylinder runs off excess solar energy, so as it’s finally decided to stop raining and we’ve had a couple of hours of early sunshine, I have 65 degree water temperature, so it may be tomorrow morning before I know if that’s worked.

If it hasn’t, and I assume the reset feeling like it’s doing nothing, would you suggest swapping the cut-out?
 
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No if the cut out feels like it is doing nothing, then it means it hasnt activated, if it had activated you would feel a click when re-setting it, you dont need to change it
 
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Thanks Ianmcd

Anything else obvious to try? I struggle to get an engineer because I'm semi rural, plus I've not found anyone reliable as yet
 
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