Boiler heating hot water every 10-15 minutes?

[Fiugs]

Hello everyone.... This is my first post I do hope you can advise me...

We have had a lot of work on our oil fired CH system lately; the whole system was blocked with iron oxide sludge apparently. It is currently running with a sludge dissolver in its system for a while, after which it will be flushed...

Anyway, during the repair a few new parts were added to the system, offering us the chance to have independent control of our hot water... Now we can heat the water separately from the CH, which was previously not an option. Before we had to use the electric immersion to heat the water because the boiler was unable to heat it much as the room stat would keep the boiler off too much.

So here's my query - now that the boiler is heating both rads and hot water, it appears that the room stat is asking for heat as it always has; approx once or twice every hour... BUT the call for hot water seems to be firing the boiler about once every 10-15 minutes - even though we have not used any hot water all day.

Can anyone advise me? I have tried to locate the stat on the hot water tank (there def is one) but haven't found it so far... Although I admit so far I have only been feeling around through the insulation, which I am loathe to pull off to look...

Can anyone suggest what the cause of this frequent boiler cycling can be?

With thanks - and hello!

 

[Tibbot]

What controls have been added?

 

[Fiugs]

Hi tibbot.. That was quick! Thank you

A new 7 day timer has been added that can give me separate control of rads and HW.. And a motorised valve to enable said switch to heating HW only. The plumber said I could add another valve if I wanted to give me the option of CH only as well..

I realised after submitting my earlier post that it's supposition on my part that the frequent boiler cycling is related to the HW function. I guess i was assuming that because I called the plumber yesterday (within three hours of him leaving) to question the frequent cycling and he said it was probably just that the newly-filled HW tank (the system had of course had been drained) was still warming up..

It would be more accurate for me to simply say that the boiler is cycling every 10-15 mins, even when the room stat is not calling for heat and we have not used any hot tap water at all... Not since early this morning actually.

 

[Tibbot]

Whatever the system you should have provision for HW only. Older gravity systems meant CH only setting unavailable but always a choice of HW or HW&CH.

Your comment that the r/stat used to stop the boiler firing for HW leads me to suspect the system was wired incorrectly and may still be. For example if the boiler is mistakenly made to fire with your new HW zone valve and CH pump closed you'll get cycling. That may not be what's happened but gives you an idea.

 

[Fiugs]

I do have an older gravity system. And yes, as if yesterday I have the option of HW only or CH and HW. Before yesterday the former option was not there for me, because the ancient motorised valve (replaced yesterday) did not work. At least that is my understanding.

Pervious to yesterday, the system did also heat the water, to a degree, but because the room stat was turning off the boiler when it was satisfied the water only got hot enough on quite cold days when the room stat was asking the boiler to work harder... Does that make sense?

 

[Tibbot]

If you have a motorised valve on the gravity circuit to the cylinder it must work via a command from the HW of the programmer then cylinder stat or directly from the programmer if no cylinder stat fitted. The zone valve then fires the boiler (without the pump). The r/stat should not interfere with this process.

You can have the following systems with gravity HW

1. Simple Gravity (programmer HW or HW&CH, CH pump, R/stat)

2. C-Pan (as above with zone valve and cyl stat on HW primary circuit). This can allow provision for CH to work alone if required.

You could install a HW zone valve without cyl stat but it wont give HW temp control but will still prevent reverse circulation problems if they exist.

If yours works any other way, it's incorrect.

 

[Fiugs]

You say, "the zone valve fires the boiler without the pump"? That's the other difference since yesterday- the pump is on the whole time the timer is on. I.e. From when the timer turns the system on first thing till it turns it off at bed time the pump is running. Previous to yesterday the pump came on when the room stat called for heat, it went for a while before and after the boiler fired.

Yes... I guess I must currently have the first system you mention. Plumber said I could possibly add a CH only option.

And yes.. I'm guessing that the way things are working just now is incorrect, hence my posting this thread...

I get the feeling I must be missing something you're trying to communicate to me... Sorry... I'm just wondering why my boiler is firing so often when room stat is not calling and no hot water is being used.

 

[Tibbot]

Assuming it is still definitely gravity and hasn't been converted to fully pumped (without your knowledge), the controls seem to be wired incorrectly.

 

[Fiugs]

Oh lawks.. No idea how I would know.. Pump is beside boiler.. Always has been. If a gravity system has no pump than I guess it can no longer be a gravity system?

I'll call plumber on Monday...

 

[Fiugs]

Hi again
Just in case anyone's curiosity was piqued with this issue and someone wanted to know the outcome - and also the moral to the tale - read on...

So, the plumber came round today and explained things to me.

The reason the boiler was firing so often, even when the room stat was not demanding heat, was because the hot water cylinder does not have a stat on it. Needless to say, I thought there was a stat on it and I thought the reason I had been unable to find it under all the insulation was simply my own ineptitude.

So now I have requested a cylinder stat and another motorised valve from the boiler to the HW, so my system will have independent HW/CH control.

In effect the stat has been turning off the heating, but the boiler has still been cycling and the hotter and hotter water has been going through my statless cylinder and round the system like the magic roundabout, doing nothing but getting closer to boiling point as the day went on. Thank goodness I pursued this with him - he was treating me like I was concerned about nothing..

.. and the moral of this tale, for me personally anyway, is - never assume that my plumber will actually advise me what my system could benefit from to make it better, in fact assume that they will fit exactly what I ask for, even though it would serve little purpose without the other missing but necessary parts (I asked for a room stat to help reduce heating bills... but clearly i should have said "what else, that I don;t know about because I;m not a plumber, is necessary to add to the room stat request, for my need to be truly answered?").

I would have had no idea of what I needed to add to my ancient gravity system to improve it as much as possible had I not devoured the internet, including this forum (thanks all!). It seems, with our plumber at least, one needs to study plumbing before one knows the right questions to ask...

Well I got there in the end.. (unless there's something else I don't know because I haven't completed my plumbing apprenticeship yet!!) They're coming to fit the cylinder stat and the second valve later this week...

Hope I don't lie awake tonight wondering if there are any other magic missing questions out there...