Boiler cycling on /off every 2 mins when heating

[Steelmasons]

You should close the bypass valve and count number of turns.

Then open exactly one turn.

Tony

Exactly one turn????..that will depend upon valve manufacturer as to how far the gate travels.
Why count the number of 'turns' to close??...Obviously a moot point if opening one full turn from closed...

 

[Hugh Jaleak]

The bypass is there to provide a path for some flow at all times, to prevent the pump pushing against total resistance if circumstances allow all TRV's or the motorised valves close off with pump still running. I think regs now state it must be an auto bypass valve on new systems, (you might already have one looking at the pics).

Rattling was probably the flow trying to force its way past the gate inside the valve, you've suddenly made the pump work a lot harder and force the water round the rads instead don't forget! Bypass will still be hot, as some flow will be getting through, unless you close the valve totally.

Cylinder may well have been boiling (or close to boiling), with no thermostatic control, it can conceivably get to the same temperature as the water leaving the boiler, with stat fitted on an S plan, the stat should be set to about 65 °C, once the cylinder is up to temp it will close the Motorised valve on the HW circuit and boiler will either shut down if CH is satisfied, or put its full effort into the CH system until CH is satisfied/HW calls again.

 

[ElCI]

Hugh
Yeah that's fine I'm definitely going to go for the s plan. For my own understanding though can I clarify a few points
In the current setup surely there is no need for the bypass as there is a path for water at all times through the cylinder?
In real terms is it dodgy to fully close the bypass gate indefinitely? I have most trvs set to 5.

BTW, I don't believe I have an auto bypass at this time although I stand to be corrected, all I have on bypass pipework is the red gate valve

Thanks

 

[DP]

Exactly one turn????..that will depend upon valve manufacturer as to how far the gate travels.
Why count the number of 'turns' to close??...Obviously a moot point if opening one full turn from closed...

Steel, you are used to man spanners devoid of precision tony exercises with tweezers and tools in his bob the builder tool kit. You need to pull up your socks fella if you want to be one in a hundred, but will never be in the upper reaches unless you travel on the buses

 

[Steelmasons]

Anyone in the trade only has to read Agiles posts in order to realise he's a charlatan.
I'd laugh if he knocked on my door in order to carry out plumbing/heating/gas works...
...and yes I have met Tony..

 

[Groovejet]

What was the state of the header tank in loft? Filthy?? Draining older systems without checking state of header tank can add to a real headache.... instead of just being able to scoop out the debrie in tank then draining down.

And do you know if it is a close coupled feed and expansion pipe or is there a expansion pipe going over the top of the header tank??
Only mentioning as its possible that there is a blockage in the cold feed pipe, which if its close coupled(meaning cold feed and expansion pipe are one pipe coming of bottom of header tank) Then it will cause problems.

Apart from a visual ! You can use a magnet on the pipe to see if there is any attraction, if it is magnetic then youve got sludge in pipework.

 

[DP]

Bypass valve should be closed until you get the system converted to S Plan.
If you can, by adjusting HW valve, achieve 11 degrees across CH flow and return, you will have done well.

 

[ElCI]

What was the state of the header tank in loft? Filthy?? Draining older systems without checking state of header tank can add to a real headache.... instead of just being able to scoop out the debrie in tank then draining down.

And do you know if it is a close coupled feed and expansion pipe or is there a expansion pipe going over the top of the header tank??
Only mentioning as its possible that there is a blockage in the cold feed pipe, which if its close coupled(meaning cold feed and expansion pipe are one pipe coming of bottom of header tank) Then it will cause problems.

Apart from a visual ! You can use a magnet on the pipe to see if there is any attraction, if it is magnetic then youve got sludge in pipework.

Groovejet thanks for the comment, I have no idea to be honest if it's close coupled or a separate pipe, I don't actually even know when the F&E tank in my loft is! If I went up and found would it be quite obvious if it was a separate pipe?

Also, I'm not sure about the state of the tank before it was drained, I had asked if the water was fresh in it (to work out if there was a leak in the system) and the plumber said it wasn't, take from that what you will. If it had been filthy is there anything I can do at this stage? Basically since I'm working on the system at the moment I'm looking to get as much done in 1 go as possible, I'm off overseas time a few weeks for work so I'm trying to avoid the system having major problems when I'm away
Cheers

 

[Agile]

Best take out a boiler cover insurance scheme then!

 

[DP]

Mmcgar, issues you have with the system, very easily resolved by repairers but combi bashers will no doubt struggle

We are at page 5 still arguing if the bypass should be precisely opened one full turn or totally closed when full flow will always be achieved to HW primary. Someone who is hands on will be able to resolve the issues without sweating and also advise you how better controls will lead to economical running of system

Noises you hear from the system, could well be pump over or air sucked down the vent pipe, issues a competent repairer like Ian, Pullar and few other regulars here could address one hand tied behind their back.

 

[ElCI]

DP, I tried to DM you there but you don't seem to have the option to start a conversation on your profile, if you or any of the guys you mentioned cover my area and want to send me a DM please feel free.

In terms of the noises etc I'm not overly concerned by them I just want a boiler that functions normally. I had been a bitpremature last night when I said that altering the hw gate valve had helped, it must have been the fact that it was full of cold water that had made the difference as this morning it was back to normal with a roasting hot return pipe and the boiler cycling after 15 mins of operation.

I had a look at the installation manual for my boiler, see picture. It seems to confirm what you said, I don't actually need the bypass in the current setup as I have no thermostatic control of the hw so this will effectively act as a bypass. But when I install the S plan system u will need it. It does also mention that the bypass should be 8m of pipework, id say it's lucky if it's half if that!

 

[Agile]

The idea is that the bypass piping will actually dissipate some heat from the boiler to cool that down if there is no open path.

I specifically give a basic setting for a gate valve bypass so that is available for anyone casually reading this in the future. Of course in your own case it is irrelevant until your system is reconfigured and could be completely closed just in your particular case.

As we have explained, in your case the boiler has to modulate on/off and if it is running for 15 min then that may well be totally correct for your boiler output and heat absorption.

Tony

 

[Hugh Jaleak]

I beg pardon, looking more closely at the picture and I realise what I mistook for an auto bypass is actually a bleed point.