Boiler on/off short cycling

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spatel

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Hello,
Require some help and advice.
Whenever I turn on my boiler for hot water or Central heating, the boiler turns off for a few minutes and then on again. This cycle repeats itself every 5minutes.

I recently had my systems flushed with many of the radiators installed with TRVs as well as an old rad removed upstairs and replaced with a new bigger rad (with pipework carried out under floorboard).
I have noticed that there is a constant trickling noise from the rad closest to the boiler and no matter what I do to relieve the air from the rads, the boiler cuts out and one of the rads is not heating up efficiently. The other rads are also making a knocking sound too, though remain hot when the boiler is on.
Sounds like air in the system but plumber ensures me that all air has been removed and is not sure why the rads are making this noise or what the trickling sound is.

Any advice would be appreciated,
Thanks!
 
you will have to give a lot more information, boiler make and model ? system sealed or open vent ? Y plan ? S plan ?
 
Hi Ian,
I believe I have an open system, with a hot water tank in airing cupboard and the header tank and cold water storage tank in the loft. The boiler is a Main 24 HE (Baxi potterton). I am not sure if its Y or S plan. I can find a motorised valve for the HW connected to the HW tank but cannot find a valve for the CH (could be hidden somewhere). One other thing I have noticed is there is a lot of air accumulating in an upstairs Rad (even though I continue bleeding it everyday - after the system is cooling day). The trickling sound from the rad downstairs near the boiler is quite prominent. Hope this helps and any advice appreciated.
Thanks
 
I think you are mistaken, if you have a Main system HE it should not be open vent, they are only designed for sealed systems, post some pics of your boiler and HW cylinder set up and the valve you speak of so I can see what you have
 
Thanks Ian,
Apologies for my knowledge in the plumbing field is minimal.
Here are some pics of the system (minus the loft set up).
Setup:
Boiler - Kitchen
HW cylinder: Upstairs airing cupboard (inc motorised valve)
H20 Pump: Cloakroom (next to kitchen)
Radiator making trickling noise - Kitchen (closest to boiler)

Also the boiler has been turning itself off with the overheating error symbols indicated.
Just trying to figure what it could be (h20 flow, airlock , leak).
Thanks
 

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Your boiler is a Main Heat only High Efficiency condensing boiler and is suitable for the open vented system that you have, the trickling noise that you describe on the rad closest to the radiator is likely to be a lockshield issue usually can just be sorted by adjusting it, the boiler on off cycling really needs a professional to have a look, can be a few things but none of which are DIY
 
sorry meant to ask do the radiators heat up when you have this short cycling ?
 
Thanks Ian.
The rads do heat up though one of them does not very well. Warm at top cold at bottom. And another rad upstairs is cold on one side. Airing helps that one but then the air returns again once the CH is turned on again. I also hear trickling noise in the boiler too or at least around the pipes and magna filter as well.
 
There are a few things that can cause your boiler to short cycle, but as said none of them unfortunately are diy repairs, and we are not allowed to advise you in this open forum how to check them
 
No worries Ian. I understand. I merely try to help out my plumber as he is not sure why it is short cycling and the other issues. I am happy to give you his details so you can DM if you are ok with this?
 
OP, you are describing symptoms of low water flow through the boiler, possibly as a result of a poor power flush?
Could it be that the overflow from your loft tank runs when the system is hot?
Could it be that the power flushing solution has been left in the heating system, causing large amounts of CO2/air to be liberated within the rads?
Could it be that your Magnaclean is blocked with debris?
Could it be that your pump is blocked, or has failed in some other way?

MM
 
Thanks for the suggestion MM.
1. Will need to check with plumber about the overflow.
2. Plumber didn't really do a power flush as such. I think he did a system flush. Guessing that is a drain down and refill. The house is old with narrow pipes. Concern was a power flush could be cause more damage than good. He refilled with Fernox. Concern is that I constantly need to bleed air from a rad upstairs. Ian suggested that air is being drawn into the boiler somehow. So need to figure out how this is happening given that plumber simply did a drain down to fit a new Rad and install TRVs on all the others.
3. Plumber checked the Magnaclean, I saw it too. It looked pretty clean.
4. Plumber check pump too and that looked fine (according to him).

Before we had the work done last week, we had absolutely no probs at all with the system. All rads worked very well and no probs with boiler either.
Just wanted to get TRVs to control heat and put a bigger rad in room. Now we have all these issues!

The mains symptoms that worry me are:
1. The constant need to air a rad upstairs
2. Why a rad downstairs is lukewarm at top and cold at bottom
3. Why some of the rads now make a knocking sound
3. Constant trickling sound from a rad close to the boiler
4. trickling sound coming from the boiler when starting on and turning off
5. Overheating off the boiler when HW + CH is turned on
6. The short cycling of boiler.
7. IS there a leak created that leads to all these symptoms (and where that might be!)

I am worried that the whole thing could a massive problem!
 
Did the system refill easily after the draindown? Possible blocked feed pipe from loft tank?

Does the feed pipe join the heating system immediately before the pump?
Will a magnet adhere to the copper pipe at this point?

Is the vent pipe close to the fill pipe, or are they combined?

Is there evidence of pumping over? (discharge from the vent over the loft tank).
Does lowering the pump speed stop the pumping over?

These are questions for your plumber.
 
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