Boiler cycling - continuing problems!

[xMeta4x]

Hi All,

I've just had a blocked cold feed remedied (cut out and replaced with plastic pipe for some reason).

With that done, I still have an issue with my boiler (Potterton profile 60e serving 11 radiators) cycling whilst heating the system. Once the room stat is satisfied it turns off as expected.

It cycles on for 2 mins, off for 2 mins. Is this normal? I have the stat set to max as I want the house to heat quickly.

It doesn't lock out such that it has to be reset, only cuts out normally.

Any help/clues?

Cheers,

Andy

 

[bengasman]

no, not normal. once the roomstat is satisfied, the pump should run for a few more minutes, but never come back on again until the roomstat calls for heat again.
unless the cylinder is calling off course

 

[xMeta4x]

I thought not. What could cause this? The pump appears to be running freely and is set to max speed.

Is the pump knackered, or is the boiler stat shot?

Cheers,

Andy

 

[bengasman]

pcb has a bit of a reputation on this boiler, so from a distance would be my first guess.
hard to say from behind a keyboard, really need to be there and go through fault finding process

 

[namsag]

Does it still cycle when the programmer is not calling for heat if so you may have a stuck microswitch in the motorised valve .

 

[xMeta4x]

@bengasman - That was my first thought, is it a DIY job to replace? I don't believe I'd need to open the case so no need for a CORGI...?

@namsag - No, when the programmer, room stat and/or tank stat aren't calling for heat it doesn't cycle, it stays off. It only cycles when there's a genuine demand for heat.

Any further insight greatly appreciated!

Cheers,

Andy

 

[bengasman]

it is arguable whether or not it is diy work.
no, you don't have to open gas or flue parts, but you are still working on a boiler which theoretically makes it corgi terrain.

on a more practical side, a pcb does not come cheap, and it takes little to kill them.
unless you are skilled with electrics and electronics, i would say: don't try yourself. purely from a wallet point of view. besides, you think it is the pcb, but you don't know it.
heating engineer replaces a board and does not cure the fault, he pays for the board.
at least he should. my clients pay me for solving the problem, not for drinking tea, talk about the weather or wonder why the blasted boiler is not working.

 

[twgas]

as you've had a blocked cold feed, I would suspect that some of your pipework, probably between the cold feed and motorised valve(s), is partially blocked and thus reducing the circulation rate hence the boiler getting up to temperature very quickly.

 

[xMeta4x]

@bengasman - Thanks for the advice, if I get the PCB changed I'll get a CORGI in to do it.

@twgas - The system blasted the draining hosepipe off when the supply to the F&E tank was turned back on (following a drain down) so there seems to be good circulation! I'm going to run some X400 through it, followed by some X100 so hopefully that will resolve/eliminate the possibility. The rads heat up fine so just the boiler cycling that seems to be an issue.

Other than that (which I'll try), anything else that I should watch out for other than circulation (sludge/pump) and boiler electronics (PCB/Thermostats)?

I'll go for the X400 first as it's cheap and easy - can I just add it to the F&E tank and drain through a few litres to get it into the system?

Cheers,

Andy

 

[bengasman]

obviously, if you supply the pcb and it does not solve the problem, the engineer will say................
and he would probably be right as he will buy the parts form an trusted supplier, and not from an internet shop based in poland

 

[xMeta4x]

OK the X400 is in the system, and I took the opportunity of the partial drain to clean out the brown crud in the F&E tank.

I noticed that the pump (old celsia multihead) is weeping from the lower union so that will be replaced with a grundfos when I drain the system down and flush after the X400 has done its job.

As the boiler is kettling a little should I run a de-scaler through as well, or is it more likely that the pump possibly being knackered is causing the kettling as well as the cycling?

Cheers,

Andy

 

[xMeta4x]

An update - I flushed the X400 and added X100 and X200 to the system, and replaced the pump with a grundfos UPC 15/50 at the same time.

The system heats up much quicker now with less, but still some cycling. I'm assuming that the return is getting up to temperature and cutting the gas etc.

Hopefully this is the end of my little saga!

Andy