It there an automatic bypass valve fitted, and are the pipes to/ from it hot when the boiler starts cycling?
Boiler cycling on /off every 2 mins when heating
- Thread starter Mmcgar
- Start date
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Not sure if there's a bypass, I'll attach a photo of the setup.
Yes the pipes to and from the boiler are very hot when cycling starts
Yes the pipes to and from the boiler are very hot when cycling starts
Actually I assume that red isolator on the right hand side is a bypass. If it is it is fully open, is this correct?
When I see a system with compression fittings with PTFE tape inside I think of DIY.
The gate valve in the middle is the bypass. That should be closed and opened half a turn until a flow can just be felt by the heat on both sides of the valve.
But that valve setting should have been checked by the boiler installer and the valve head removed! Or has the OP been fiddling?
Tony
The gate valve in the middle is the bypass. That should be closed and opened half a turn until a flow can just be felt by the heat on both sides of the valve.
But that valve setting should have been checked by the boiler installer and the valve head removed! Or has the OP been fiddling?
Tony
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Good chance, if no other motorised valve, cylinder acting as a bypass also, so for the time being, I would close the bypass gate valve, restrict the gate valve to cylinder for correct working delta t
Tony, does it really matter if the OP has been fiddling? Who cares, I don't.
By the way, not for the first time, nor will it be last, I have used ptfe tape myself.
Tony, does it really matter if the OP has been fiddling? Who cares, I don't.
By the way, not for the first time, nor will it be last, I have used ptfe tape myself.
DP said:
It might matter in the sense that it might be the cause of the excessive cycling.
That is true, but I would give the OP benefit of doubt. I have seen some strange lashups recently causing all sorts of issues
Couple of weeks ago was sorting one system where boiler was doing exactly what OP says. 28 mm primaries to a cylinder with red jacket. No wonder heating was poor and boiler kept cycling. Mind water was nice and hot
Hi all
I have been away the last few days so only just catching back up on this. Can I ask a few things please, also just to be clear I have not personally done any diy on this, I know my limitations and generally don't touch stuff I don't understand
Should the isolater on the right hand side of my picture be closed? I am sure it is fully open at the moment, I can try and find out if the plumber who worked on the system recently done this but I have not been able to get hold of him...
I have checked the temperatures of the return pipes, it definitely seems to me like the return from the cylinder is much hotter than the return from the radiator manifolds. This led me to suspect that the cylinder is effectively short circuiting the system and returning the majority of the water to the boiler?
I have had to bleed the system again, 3rd time in 10 days, I keep getting a water rushing and bubbling sound from the pump and cylinder when the boiler stops. This seems to be fixed when I bleed the system but starts again a few days later.
Also I have attached a picture of the boiler controls, it seems the thermostat is set to 3 (of 6) I'm not sure if this is low or not.
Finally, I do intend to get someone out to look at this, I'd like to speak to the original plumber 1at and try to identify if anything he done is causing this
I have been away the last few days so only just catching back up on this. Can I ask a few things please, also just to be clear I have not personally done any diy on this, I know my limitations and generally don't touch stuff I don't understand
Should the isolater on the right hand side of my picture be closed? I am sure it is fully open at the moment, I can try and find out if the plumber who worked on the system recently done this but I have not been able to get hold of him...
I have checked the temperatures of the return pipes, it definitely seems to me like the return from the cylinder is much hotter than the return from the radiator manifolds. This led me to suspect that the cylinder is effectively short circuiting the system and returning the majority of the water to the boiler?
I have had to bleed the system again, 3rd time in 10 days, I keep getting a water rushing and bubbling sound from the pump and cylinder when the boiler stops. This seems to be fixed when I bleed the system but starts again a few days later.
Also I have attached a picture of the boiler controls, it seems the thermostat is set to 3 (of 6) I'm not sure if this is low or not.
Finally, I do intend to get someone out to look at this, I'd like to speak to the original plumber 1at and try to identify if anything he done is causing this
Sorry forgot to add the picture 
DIY = Dodgy Installer Yesteryear
There was a Corgi Guy near here ( now retired ) who used PTFE on almost every joint he made.
No fiddling by OP!!
Mmcgar, do you have a motorised valve on loop to cylinder? If you select CH on the programmer, do you get water circulating to the cylinder coil? If not, run CH on its own- do the radiators heat up better?
The gate valve on the cylinder loop, close that gate valve a little, have a cuppa to allow system to stabilise, then check if return from cylinder and CH is similar temperature
With system running, check you header tank. Is the water in it hot? The air you are getting in the system may will be due to incorrect plumbing of header tank allowing air to be drawn into the system when pump kicks in
Last edited:
Thanks guys.
I have turned the left hand gate valve (on cylinder return pipe) down by 1 full turn, I'm not sure if that'll be enough but I'll do a bit of trial and error on it.
I have not touched the right hand gate valve (on bypass pipe) as I'm not entirely sure what it is supposed to do and as someone mentioned earlier this is normally set by installer and then has the head removed to prevent tampering, from this I'm guessing it's not something I should be doing trial and error on so I'll see how return pipe valve goes 1st.
In regards to the motorised switch I will attach a photo but basically my options are: hot water only, or hot water plus central heating. There is no way of running central heating only. Also the cylinder doesn't have a thermostat on it so when boiler is on the cylinder just continually heats.
Thanks again
I have turned the left hand gate valve (on cylinder return pipe) down by 1 full turn, I'm not sure if that'll be enough but I'll do a bit of trial and error on it.
I have not touched the right hand gate valve (on bypass pipe) as I'm not entirely sure what it is supposed to do and as someone mentioned earlier this is normally set by installer and then has the head removed to prevent tampering, from this I'm guessing it's not something I should be doing trial and error on so I'll see how return pipe valve goes 1st.
In regards to the motorised switch I will attach a photo but basically my options are: hot water only, or hot water plus central heating. There is no way of running central heating only. Also the cylinder doesn't have a thermostat on it so when boiler is on the cylinder just continually heats.
Thanks again
Those 2 pipes going through the ceiling in the picture, do they feed the cylinder? I wondering if now we start to see your problem, the flow will be taking the easiest path, which by the looks of it, is through the cylinder. Before you do much else, I would get the system altered to 'S' plan if this is safely possible. This means fitting a cylinder thermostat and motorised valve to the cylinder pipework, so when cylinder is up to temperature, full flow can be put into the radiators.
However, (I am assuming you system is open vented), there must be a clear, continuous upward path from the boiler to over the F&E cistern, if this is currently done using the cylinder pipework, a valve cannot be fitted into that section of pipework.
However, (I am assuming you system is open vented), there must be a clear, continuous upward path from the boiler to over the F&E cistern, if this is currently done using the cylinder pipework, a valve cannot be fitted into that section of pipework.
Hugh, that is something I had considered previously, I had read on other threads on this forum that some baxi boilers don't work well with 3 position valves. Of it is relatively inexpensive it's something I'd happily get done right away, my thinking is that with the age of the boiler and other issues it's had I'm probably going to need to replace it in the short term anyway so if fitting the thermostat and valve is expensive there's probably not much point. I am trying to get hold of a central heating engineer just now to come out but haven't had any luck so far, if I do get hold of 1 though I will ask him about it.
Also, I got hold of the plumber incised previously and they say they definitely didn't touch the bypass or cylinder gate valves so it seems the bypass has always been fully open
Also, I got hold of the plumber incised previously and they say they definitely didn't touch the bypass or cylinder gate valves so it seems the bypass has always been fully open
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