Gravity hot water not circulating please help

[gasmannn]

I had a problem with no hot water on a gravity circulation system, I thought the coil was blocked as it was getting hot to one side, so I changed the cylinder, still didn't work, I then found a two port valve boxed in and the head was gone so I replaced, started to fire but still hot to only one side of the coil, tried back filling through the boiler drain off got some heat round the return while filling with boiler running but once I stopped and tried running it again still won't circulate????

 

[Billy Bob Bob]

cold feed blocked or ballvalve jammed

 

[gasmannn]

There fine drained system 3 times now and has filled up every time

 

[gasmannn]

I've heard you need a special cylinder for gravity which I did not no when I replaced it could this be the problem ??

 

[Billy Bob Bob]

normally you need one with a 28mm coil

 

[Billy Bob Bob]

what set up is it gas or solid fuel?

 

[gasmannn]

It's got 28mm coil

 

[gasmannn]

Gas has a cylinder stat if fine , time clock is fine, it fires on hot water only for long enough to heat the flow to the coil but won't return through Coil. Ive turned of cold feed and capped open vent tried backfilling because I was told can block near boiler, still does nothing, I tried boiling it by removing boiler stat does nothing

 

[snowhead]

Have you had the 2 port valve body apart / out to look inside?

 

[gasmannn]

No just change the head as I found this was faulty it was hidden in boxing away from the boiler do I thought there were no controls, i move the spindle and it seemed to be free of any blockage

 

[Billy Bob Bob]

you have a airlock by the sounds of it,it will take some balls and you need to be very careful in what your doing but removing the stat(if its a older boiler) for a few mins should sort this but do not attempt this if your unsure other than that try cracking the return nut see if you remove any air

 

[Billy Bob Bob]

just seen the part about the valve this on the gravity circuit?

 

[gasmannn]

I have removed the stat and boiled it heard a lot of air and banging but did nothing also have cracked both nuts on the coil both have water?

 

[gasmannn]

Yeah it has a two port valveon the gravity

 

[Billy Bob Bob]

Yeah it has a two port valveon the gravity

you need to cut it out think thats your issue

 

[gasmannn]

I lowered the flow pipe to the coil about 2inches to fit the new cylinder but did not put any bend or fittings just a straight connector and cut a bit off the pipe

 

[Billy Bob Bob]

I lowered the flow pipe to the coil about 2inches to fit the new cylinder but did not put any bend or fittings just a straight connector and cut a bit off the pipe

on gravity flow should rise slightly and drop down to the coil but sometimes we have issues with the pipework config doing this,not caused me any problems in the past

 

[vern]

Yeah it has a two port valveon the gravity

Is valve on return I.e C plan with cold feed and expansion in correct place?

 

[gasmannn]

There is no drop down just connects to coil at a level height but there wasn't before

 

[AWheating]

normally open zone valve?

 

[gasmannn]

The valve is on the return after the cold feed( this joins in to return near near cylinder coil) and there is a cylinder stat which is fine

 

[gasmannn]

The zone valve opens only when hot water is called for by programmer

 

[vern]

The zone valve opens only when hot water is called for by programmer

You have a C plan then, valve can stay is valve 28mm should be? cylinder stat should open valve if working and calling......how do you know valve is not stuck on seating?

 

[Worcester1]

There wasn't an antigravity valve in the return was there?, had this before and it
Had seized

 

[gasmannn]

Valve is 28 mm and I turned the spindle with grips it was ok

 

[gasmannn]

On the flow there is some type of fitting that is compression that has a cap on and feels like there is a spring in it,but the pipe gets hot above and below this??I don't know wat it is someone said it is an old pressure relief is this true?

 

[gasmannn]

On the flow there is some type of fitting that is compression that has a cap on and feels like there is a spring in it,but the pipe gets hot above and below this??I don't know wat it is someone said it is an old pressure relief is this true?

 

[vern]

Valve is 28 mm and I turned the spindle with grips it was ok

Sounds like a really bad airlock, or cylinder coil is too high a resistance?

 

[gasmannn]

I've boiled it through to clear air and cylinder is no higher than previous and I assume it's work s for years

 

[vern]

I've boiled it through to clear air and cylinder is no higher than previous and I assume it's work s for years

No I meant coil resistance not cylinder height, did you order cylinder specially as they are not generally available since part L came in, deffo a full bore 28mm gravity spec coil?

 

[gasmannn]

Just a normal cylinder I'm afraid I'm 23 and have not worked on these before really I naively thought this would be ok, I the only option a different cylinder? I've lost all profit in the job already I've been so long trying to fix it

 

[Best]

Some cylinder coils are not for gravity. I remember Range cylinders said on their books that you had to specify a cylinder for gravity. I think ordinary cyl had too level a coil. Ask manufacturer.
Do check the primaries are gradually rising & falling without the least wee dip. A droop in a flow pipe of an inch will stop flow.
I take it you didn't drop the flow or return a bit below the floor when you fitted cylinder?

 

[vern]

Just a normal cylinder I'm afraid I'm 23 and have not worked on these before really I naively thought this would be ok, I the only option a different cylinder? I've lost all profit in the job already I've been so long trying to fix it

That your problem then pal, you will have to have one made, unless you can find one at a suppliers gathering dust, failing that convert to fully pumped, or talk them into a combi
don't worry we all f£ck up from time to time, valve you mention earlier is a spring loaded pressure relief valve should the expansion block up and boiler stat fail
good luck sorting...

 

[gasmannn]

Some cylinder coils are not for gravity. I remember Range cylinders said on their books that you had to specify a cylinder for gravity. I think ordinary cyl had too level a coil. Ask manufacturer.
Do check the primaries are gradually rising & falling without the least wee dip. A droop in a flow pipe of an inch will stop flow.
I take it you didn't drop the flow or return a bit below the floor when you fitted cylinder?

The return fitted ok but the flow was a bit higher so I just dropped it with a straight connector no elbows or bends

 

[AWheating]

you can still buy cylinder with gravity coils from most merchants, its what they use on solid fuel installs. grade 1" gravity coil cylinders, prob cost abit tho.