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I noticed it coming on at apparently random times, now it seems it's heating the hot water all the time. 5 year old house with a hot water tank, timer is set to come on for an hour late morning.
The only thing that happened recently was that I noticed the pressure in the system was way low so I opened the taps to re-fill it. Also I slightly tweaked the temperature control knob on the thing sticking into the tank - but I think that may just be the immersion heater anyway.
Timer knackered? Boiler control unit knackered? The water is extremely hot.
Obvious question - have you somehow set the immersion to "on"?
First step would be to switch off any other water heating, empty the tank and see if it heats up again.
The boiler is going, even though the timer is set to off and the little led is off. Must be the timer that's gone bananas. Unless there is some reason the boiler would be making noises when I'm not expecting it?
Gas valve stuck? It will keep going until it boils. You might see venting up by your header tank and hear bubbles going up the pipe.
Call an engineer.
Mine starting doing something similar - heard the boiler kicking in when it wouldn't normally. when the boiler was serviced the plumber asked if i needed too be heating the water all the time...
Turns out my son had set the temperature to max and in doing so it also sets the boiler to keep it warm.
I am no plumber - but it sounds similar 🙂
Neighbour had something similar, boiler kept kicking in at odd times, builders had plumbed the toilets into the hot feed......
I think the controller is borked. Came back from a long weekend, fuse had blown. Replaced it, boiler was always on. Turned the heating on and off, the motorised valves are moving, but I have no idea if they are right.
In any case, surely the valves being stuck would not cause the boiler to run even when the controller says it should be off? I'm not talking about the water getting hot when the heating's running, I mean it's ALWAYS heating the water regardless of what the controller is programmed to do.
Anyway, question #2 - what to look for in a new controller? Anything fancy I can do for energy saving?
Bump, any plumbers on the day shift?
Also I slightly tweaked the temperature control knob on the thing sticking into the tank - but I think that may just be the immersion heater anyway.
I was thinking about this a couple of days ago.
Our old pressurised HW tank had thermostats for the oil ch boiler and the electric immersion heater on the tank itself at the bottom.
It would be worth double checking that you haven't turned up the boiler controller on the tank. If it's set too high, it could be calling for heat (making the boiler fire) even if it's boiling off the top.
Worth checking anyway.
Yeah but the hot water is meant to be OFF at this point.
does the boiler ever switch off by itself?
if yes, my guess borked timer, sounds like the output is stuck on.
or
if no, possibly that the overrun stat has gone
usual disclaimers, I am not a plumber, etc.
When I posted this thread, no, it didn't switch off. It was running for ages, I had to turn it off manually.
However, it seems to be behaving itself now - I turned both the water and heating on, then heating off, and that seems to have done something. Sticky relay or something..? I'll google for overrun stat.
Could well be the relay.
BTW when I said overrun stat, if this had gone, it would only run the pump (the boiler itself wouldn't be burning). So if the boiler was on then it won't be this...