Boiler cycling

[dave1]

I've ended up with this job and a little bit stuck at the moment. I'm hoping one of you guys can help.
It's a suprima 40, the heating now works fine after new rad valves and a balance of the system.
The hot water is where I'm stuck, the boiler cycles on and off for well over an hour until the h/w is up to temp.
What I've found so far is there is no pump over run or perm live to the boer and there is no external bypass fitted.
I've tried shutting the balancing valve on the return from the cylinder down so as just to allow a little heat through but to no avail.
What am I missing?

 

[zeebeedee]

Sounds like air or a blockage in the cylinder!

 

[mountainman]

Maybe it's gravity hot water!

 

[dave1]

Cheers guys for quick responses, definatly not gravity hot water, and I don't think there's a blockage or airlock as flow and return get very hot.

I think it's just a matter of balancing the hot water correctly, as the thermistor is on the flow, I think it's a matter of getting it right so the water doesn't fly around to quick and not to slow so the flow gets too hot too quick.

 

[zeebeedee]

I have never even heard of balancing the hot water!

 

[mountainman]

I have never even heard of balancing the hot water!

Used to be a consideration back in the olden days.

 

[mountainman]

Perhaps the cylinder is full of scale.

 

[dave1]

That's an idea mm, so you think they're getting less hot water then expected?
That wouldn't make the boiler to keep cycling though, or why would it make the h/w take so long to heat up?

 

[diamondgas]

Hi Dave1 ... Sounds like circulation probs, first thoughts! Before the boiler lights up grab hold of the f&r pipes. If the 'f' gets hot rapidly then your circs have a blockage and/or the pump's defunked!!! IMHO

 

[dave1]

Ok cheers diamondgas, I think I'm looking into it too much and missing something more obvious, maybe coil scaled up.
The only thing that's putting me off that is the fact the return at the boiler gets hot relatively quite quick.

 

[diamondgas]

Ok cheers diamondgas, I think I'm looking into it too much and missing something more obvious, maybe coil scaled up.
The only thing that's putting me off that is the fact the return at the boiler gets hot relatively quite quick.

Return getting hot "relatively quick" could be a bi-pass open? As long as f&r are heating relatively evenly (11 DegC Diff therabouts) Circulation is good! The suprima cycling could be down to an over sensitive stat? I'm not sure off top of my head whether they have a time delay incorporated in the PCB regards cycling?

 

[dave1]

There is no bypass fitted mate.

 

[diamondgas]

There is no bypass fitted mate.

No bi-pass, or even with, then I tend to look for a gradual and even increase in temp regards f&r, especially in hot water only mode. End of day you have at least 22mm circs, full bore without any balancing valve! You'd expect a relatively even rise IMO!

However if that is what's happening over the hour you state then you don't have an issue Dave except maybe an over sensitive stat or issue with anti cycling mode if it's present?

 

[Nostrum]

feel the flow and return at cylinder coil, if you can't get a decent differential across the 2 with a cold cylinder then something is stopping the heat transfer process, scale on the inside would be a good reason.

Most systems don't have a balancing valve on cylinder return and work reasonably without short cycling.

 

[Nostrum]

Can't believe it took me over 13 mins to reply to that!

 

[diamondgas]

Can't believe it took me over 13 mins to reply to that!

?????? ... 13 mins? My response was 29 mins after ..... lol

 

[Nostrum]

I give up!

 

[buckley plumb]

where is the cold feed teed into - could be on the cyl rtn and this could be blocked - worth a try

 

[dave1]

where is the cold feed teed into - could be on the cyl rtn and this could be blocked - worth a try

Nah it's tee'd in before the pump in the flow.
Could I be right in saying if the coil (external) is scaled up it would take a long time to heat the cylinder?

 

[diamondgas]

Nah it's tee'd in before the pump in the flow.
Could I be right in saying if the coil (external) is scaled up it would take a long time to heat the cylinder?

Yep! AND F&R would have a significant diff in temp especially from cold! I harp on about temp diff but it can tell you sooooooooooooo much about how the system is working .. honest

 

[buckley plumb]

Nah it's tee'd in before the pump in the flow.
Could I be right in saying if the coil (external) is scaled up it would take a long time to heat the cylinder?

as others have said are you feeling the f&rtn at the cylinder coil as well as the boiler .had thorn olympic that cycled flow to cyl coil got hot quick and so did boiler rtn but from boiler up wards so boiler was dispersing heat up rtn as the flow was restricted on the cyl rtn tee to htg.you could drain and flush water through coil to check for flow and disconnect flow and rtn at boiler and flush water through them from cyl to check for blockages.

 

[RGII79]

I have never even heard of balancing the hot water!

balancing valve on a indirect cylinder coil you never heard of

 

[RGII79]

the only thing you can rely on with the suprima is thats it going to cycle

 

[dave1]

balancing valve on a indirect cylinder coil you never heard of

Glad it wasn't only me, guys thanks for all the advise so far just goes to prove what a great forum this is.
My next visit there I'm going to check temperature difference at the cylinder and boiler, also check what temp I'm actually getting out of the boiler.
If all checks out ok, think ill look at putting a new cylinder in as I think that could be the main cause of the h/w taking so long to heat up.

 

[diamondgas]

Glad it wasn't only me, guys thanks for all the advise so far just goes to prove what a great forum this is.
My next visit there I'm going to check temperature difference at the cylinder and boiler, also check what temp I'm actually getting out of the boiler.
If all checks out ok, think ill look at putting a new cylinder in as I think that could be the main cause of the h/w taking so long to heat up.

Let us know how you get on mate