Perplexing Hot Water Problem.

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27 May 2021
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I hope someone can help with a perplexing problem I'm having with my hot water system. I have a Worcester outdoor oil boiler.

My hot water schedule is set for 6am to 10am and 5pm to 10pm. The boiler will always come on at 6am and at 5pm, but it is not able to keep the water up to temperature during the "on" part of the schedule. So once it has heated the water up, it won't fire the boiler again until the next "on" cycle, in the evening. This means we usually run out of hot water during the day.

If I want to boost the hot water, I need to switch the thermostat off and on again, which is, obviously, not ideal...

There are a few things I'm reasonably certain of:

I don't think it's a problem with the cylinder stat, because I swapped it out for a brand new one, and it works perfectly when the schedule first heats the water.

I don't think it's a problem with the controller. I originally used a Nest Learning Thermostat. As part of my attempts to trace the problem, I had it swapped out for a new 2 channel multi-purpose programmer, and I still have the same problem.

I don't think it's the motorised valve because it works perfectly when the schedule first heats the water. I think that if it was faulty I would, at least occasionally, wake up with no hot water.

As far as I can tell, this only leaves the boiler itself, but it also works perfectly when the schedule first heats the water. I understand that there is also a thermostat on the boiler, but I'm not sure what, if any, impact this might have on my problem.

I hope the above makes sense! I really would be grateful if anyone can offer any insight as to what might be going on.
Thanks in advance.
 
Last edited:
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About 60°
 

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What temp are you running the boiler at ? thats a cylinder stat.
 
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About 75%, I think.
 

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Try running it on max and see if it improves the reheat time of the cylinder.
 
Cylinder looks old. Could be scaled up.
Have you measured how much hot water you get from it before it runs cold?
 

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