Search the forum,

Discuss no circulation gravity primary (semi grav) in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Status
Not open for further replies.
N

napalm1967

Have fitted new gravity cylinder to old oil fired potterton boiler 15 years old approx.it has 1inch coil inside to match old.the old cylinder was repalced as leaking at seam.There was a pump added to the primary which was removed when fitting new cylinder as I was told this made no difference to the orignal fault which was cylinder not heating up hot water but heating ok.The heating system is an old one pipe system with a mixture of pipe material LCS/copper the flow and returns are 2inch 20 rads of which some are old collum type.the heating is pumped
There is plenty of heat on the primary flow out of the boiler but it will not circulate and flow back to the boiler.
I have made sure there is no air in the coil,there are a few bends on the flow before it enters cylinder which may restrict flow a little but i dont think it would be enough to stop circulation.
the pump that was fitted before is a concern??
Would renew whole system if they had the budget!!!
I would be gratefull for any thoughts
 
If there's any dips in the gravity flow and/or return pipes you've got a chance of an air-lock stopping circulation. The pump may have been fitted to overcome this issue originally. Gravity will work fine providing there's a continual rise from A to B ... Air can trap in either the F or R. If it's in the return it can be a mare to get shot of!
 
So to summarise you have replaced a leaking cylinder that didn't heat up in the first place even with a pump fitted.

Did you check to see if the pump worked before it was removed?

Also as Diamond Gas has said it needs a rise on the pipework.

Have you tried boiling it? I will add at this point don't condone this, and do it at your own risk, but its got me out of a few tight spots. Pull the boiler stats and run until it just starts to boil and knock off, repeat at will until you get shot of the air.

Failing that I would say a pump is required.
 
Didn't realise the water wasn't heating! Might have a blockage on the gravity circs too napalm1967 ...

SimonG - there aren't many boilers left where you can make you're own thunder in the name of a repair! Those were the days!!! I'd make sure the open vent is over the tank otherwise it can get messy!!
 
Didn't realise the water wasn't heating! Might have a blockage on the gravity circs too napalm1967 ...

SimonG - there aren't many boilers left where you can make you're own thunder in the name of a repair! Those were the days!!! I'd make sure the open vent is over the tank otherwise it can get messy!!

Thats why I like working with oil boilers :)
 
Thanks all for your thoughts,the cylinder is standing next to the boiler in a ground floor boiler room and the pipes rise all the way there are 4 x 28mm elbows in the pipe work before it enters the coil and rises the short distance from the boiler.This set up worked for 14 yeras ok then the pump was added a year ago by home owners friend(retired plumber now deceased) to try and get h w to heat up this sounds like it may have improved things.The boiler is piped left hand primary - with return to right......heating flow right hand with return to left hand is this normal?The system was last drained 10 or so years ago and caused a lot of probs.The elderly lady has to bleed top rads a lot!!!so i,m thinking the system may be well and truely blocked I will put the pump back in and see if I can get some kind of movement and gentle flush out.I have the added problem that the whole system is lagged with asbestos under the floors etc.the boiler room had all of it removed in the late 80's.so i cant cause any leaks in the system.Who ever ends up with the place will have one hell of a bill.The old dear does not have the cash to much more than change boiler at most.....she may have to down size a bit
 
if you put a pump on the primary's you chance pumping over ... Would it be much of a job to remove the domestic pipes and check for blockages? Could be collecting in the bottom of the boiler. I'm guessing you'll be draining down to fit the pump yeh?
 
Pump that was fitted appeared not to be over pumping as no reports of overflow/ leaks etc.I will try drain down of system and check bottom connections do you think wet vac attached to return fittings on boiler might give me an idea of whats lurking in the bottom of boiler???
 
The cylinder is on a plinth about a metre high so the bottom of the cylinder sits at top of the boiler height and is about 500mm away from the boiler
 
If you went to the trouble of replacing your cylinder you should have added fully pumped controls as this would make the system much more efficient and work better.
 
It should circulate. I've got clients with less circ height than that and still working. If it isn't circulating its coz of some restriction. Given the age system etc its a good chance the fittings are firred/sludged up at the boiler/lowest point ....

Worth checking out if you have the access ..
 
The controls are in place ie cylinder stat,valve on primary return,programmer the only thing which could be added is room stat....but due due the lay out of property not sure it would be of much benefit
 
The controls are in place ie cylinder stat,valve on primary return,programmer the only thing which could be added is room stat....but due due the lay out of property not sure it would be of much benefit

Valve on return??? Alarm bells clang! What kind of valve, what kind of stat?
 
A picture would be very handy Napalm1967 ... Would like to know if the valve is mechanical or electrical. Either way in order of priority I'd be checking that it is functioning correctly and not restricted in any way before I dived in to the boiler connections. Catchya later in the day maybe :)
 
Hi guys....I had similar recently, you say there is no air in the coil....Are you sure? There is more pipe in a modern coil and I found thatfrom where the coil starts it may still rise inside the cylinder. The answer I came up with was to pop out the immersion and use a stick/22mm copper to push down on the top coil opposite side to flow connection. You will hear the air gurgle out, but it does take a bit of force.
 
The valve is electric honeywell operated by the cylinder stat,which is situated on the return.I had really good electrician check out immersion so i got him to give contols a look over at the same time he gave them the ok.The valve seems to operate ok and i had taken it off and had a look inside expecting a fair bit of scale but it was not too bad?/?..I will be back there this week so will try and post a pic.Will try a few more goes at removing any trapped air then start looking a perharps a blockage in the boiler.thanks to all for your ideas and help.
 
Personally napalm1967, if you've removed the pump you might as well get shot of that too, if you can. It'd only slow down the already compromised circulation.. By-the-way, those valves suffer from 'swollen ball' syndrome!:D I know it sounds painful!! LOL:D I think it's caused by the oils and greases present being absorbed into the ball inside the valve causing them to swell over time, seriously! The older the valve the bigger the balls!:) The valve still operates but the flow through it is compromised.
 
Status
Not open for further replies.

Reply to no circulation gravity primary (semi grav) in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Creating content since 2001. Untold Media.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock