Help & Advice - Vent position

[Vessy]

Hi all, this site has helped me out many times, i've tried a search but getting nothing specific to this question.

Just moved into a 1970's property, which is still in the 1970's!! after failing to successfully balance the radiators I thought I had better investigate the system to see where the problem lies, this revealed a one pipe (or single) pipe radiator system, comprising of two loops, upstairs and down, the system has been re-worked previously to a fully pumped system, removing the gravity fed HW circuit.

I have concerns as to the boiler vent and header tank feed pipework, they are connected to the primary coil pipes at the cylinder (vent tee'd into flow and feed into return)

I think I need to run the pump on setting 3 to push the water quicker round the radiator loops as the furthest radiator is dropping a massive 50 Deg F with both valves fully open, however when I do this i think i'm pumping over as the header tank was steaming hot.

I'm also concerned that the vent pipe is sealed off by the HW Valve when just radiators are being supplied.

I have attached a sketch of how it's plumbed, Pump and valves are located downstairs next to the floor standing boiler, HW cylinder upstairs with Tees to header tank pipework.



Is there a way to improve the system? is my concern about the vent closed off valid?

Many thanks.

 

[doitmyself]

Your concern over the cylinder valve is valid; it will shut off the vent when the valve is closed The cylinder valve should be in the return at the exit from the cylinder, before the feed from the F/E tank.

You say you have a single pipe system, i.e the flow and return from each radiator connects into the same pipe. Is there a by pass on each rad, so if you turn one rad off the water can still flow on to the next rad?

ON a single pipe system the flow temperature of each radiator reduces as you move along the chain.

I don't understand how you are getting a 50F drop across the last rad. The total drop at the boiler should be about 20F.

 

[Vessy]

Hi,

I like the idea of moving the HW valve to the return line, seems the simpler answer, was thinking of moving the vent line down to near the feed.

The rads are not in series, the pipe continues under the rad, meaning the rad in and out pipes join the same 22mm loop, i guess swept Tee's have been used.

I have adjusted all the lockshields to get a 20 Deg F drop, most of them are around 1 - 2 turns open, however I have one small double rad in the lounge that never heats fully, the bottom feels cooler than the top and by using a thermometer i'm reading a 50 Deg F drop accross the rad, both valves fully open. Shutting off every other rad does not improve the flow into the said rad. The radiator has been moved previously when patio doors were installed, to do this they have added 90 deg elbows into the pipework, my thoughts are that it is now too restrictive, by upping the pump speed it may force more water into the rad through the swept 'T' and give me a 20 Deg drop. Boiler flow and returns are around 20 deg F drop with all rads on, from this i'm presuming the loops are good also because every other rad gets nice and hot.

All i know is when I last had the pump on 3 for a trial the header tank was also being heated.

 

[doitmyself]

The rads are not in series, the pipe continues under the rad, meaning the rad in and out pipes join the same 22mm loop, i guess swept Tee's have been used.

The main 22mm loop is acting as a bypass to each radiator.

What are you using to measure temperatures?

Most rad valves are fully open by 2 turns from closed.

If a rad is cooler at the bottom than the top, it may be blocked with sludge. Remove the rad and flush through with a hosepipe.

A 90deg bend is the equivalent of adding another metre to the pipe length; shouldn't have any noticeable effect.

 

[Flanners]

Rip out and start again. Will cost you a fortune to run. And if it is sludged up you cant powerflush a 1 pipe syetem.

 

[Vessy]

The cylinder valve should be in the return at the exit from the cylinder, before the feed from the F/E tank.

Doing this would solve the problem of closing off the vent, however i'm guessing I could still have a problem pumping over and heating the contents of the header tank?

Would this be a better option ?

I'm using an IR thermometer to measure the flow and return pipes to each rad, thanks for the info about the rad valves being fully open by 2 turns, this I think gives more evidence that the loop flow needs increasing, however with the current pipework config running the pump on setting 3 will cause massive over pumping when just HW demanded.

I have removed the rad and all is clean, only very slight black ink build up in the bottom, system has had yearly checks, found a tag hanging on the header tank showing an inhibitor added 8 months ago. The rad does warm top to bottom, just hotter at the top 2/3 rds. This rad was found closed off when we moved in, probably because the room stat was above it !!!

Rip out and start again. Will cost you a fortune to run. And if it is sludged up you cant powerflush a 1 pipe syetem

Would love too, is it worth the cost?? Concrete floors downstairs! running cost so far doesn't seem too bad, being rural we have lpg, which is 3 times the cost of natural gas, presently it's costing about £3 per day to heat a 4 bed detached and water, I did fear worse!!

Long term plan it may be re piped, just want it working well for this winter.

 

[doitmyself]

Would this be a better option ? View attachment 296

Yes; and this would be even better (See end of post - I can't work out how to drop a pic where I want to. Any clues?)

with the current pipework config running the pump on setting 3 will cause massive over pumping when just HW demanded.

The pumping over is happening because the feed and vent pipes are after the pump, where the pressure is the highest. Moving them to the return, just before the pump, will mean that they are at the point of least pressure, so the pumping over should go away.

The rad does warm top to bottom, just hotter at the top 2/3 rds. This rad was found closed off when we moved in, probably because the room stat was above it !!!

Presumably the stat has been relocated to a more suitable position.

 

[timlaz]

Hi there. yup you will really need to run another return circuit to make this system run correctly. Its a bit of a job, as you'll obviously have to lift floor boards etc to get the new pipe work fitted, I'd also recommend that you fit a pressure vessel and filling loop and do away with the header tank. This would be your best way forward, because one pipe systems never worked even when new. Hope this helps.

tim

 

[Vessy]

Presumably the stat has been relocated to a more suitable position.

Oh yes, was moved on day one before furniture!!

Thanks for all the really helpfull advice, big extension plans for the house, new boiler and pipework will be done then, but that will be 12 - 18 months away, i'll re-pipe as per your suggestion, should give me a slightly better system for the short term.

Best regards.

 

[John Flower]

Brst bet is to repipe as one pipe systems are very sensitve to pipework alterations and this can end up with rads not working very well. Plus the rads are nearly always oversized especially the last one on the circuit due to their inherant design.
A properly designed two pipe system with correctly sized rads and boiler and thermostatic rad valves on all rads bar the one in the room with the roomstat will be a better bet in the long term. Also a sealed system would be a good idea too as it will negate the possibilty of air ingress and the need for a feed and expansion pipe ect.