Reverse circulation to cold water feed from cylinder

[Dboing]

Hi all new to this so pse excuse,
I have a conventional indirect coil cylinder on a open vented system running off a suprima boiler.
Cylinder was leaking, cant afford new one at mo so drained down removed cylinder and repaired. Re-fitted, filled system heating coil flow and return ok, secondary stored water hot and ok, domestic hot and heating working well after bleeding but have got reverse circulation from cylinder secondary hot up the cold feed to expansion tank. Have bled feed pipe from drainoff cock, turned down cylinder and boiler stats to eliminate over heating, have bled at pump. None of which has helped. Unfortunately both domestic and heating ballcocks have gone pear shaped today so will strip try to repair or renew 2morrow. anyone got suggestions why i have got this reverse circulation and or any remedies greatly appreciated. thank you.

 

[ChrisR]

What exactly are you describing as reverse circulation?
Some convection of heat up the feed pipe is normal. If you had flow it would overflow..??

What are "b*****s"?

 

[Dboing]

Hi chris chears for the reply,
the typo is "Ball cocks". The convection is that bad it is heating the expansion tank so cold water drawoff at bathroom basin is luke warm, pretty sure there is no flow.

 

[Dboing]

Thinking about it the domestic ball cock is not working now but was yesterday, it wont close orrifice must be knacked. but i did have a bit of over flow before the ball cock stopped working so maybe i have got flow but quite a slow.

 

[ChrisR]

Oh you mean the main cold water cistern is getting warm - not normally called expansion tank!

Is the heating header tank level above the CW cistern level? If so expect the coil is passing water from CH to Domestic HW.

Otherwise check immersion heater isn't boiling the water and sending it up the vent, and check vent is clear of water in the DHW cistern.

 

[Dboing]

Chris, chears i suspected that i may of damaged the coil when repairing "or not in this case" lesson learnt. i take the only thing for it now is to replace cylinder.

 

[ChrisR]

Fraid so.

 

[Dboing]

Morn chris, thanks for your help and advice in the early hours. Pushing the boat out now, due to cistern ball cock not shuting off i turned off the mains last night. during the evening with toilets being flushed etc cistern and heating expansion tanks lost water (expected). This morn i have turned on the mains to fill both tanks and then turned off mains, I am running the system for both heating and domestic hot which seems to be running normal, my question " with the mains off, if the coil is passing water surely the cistern will start to fill an eventually overflow the heating expansion tank empty, given no domestic hot is drawn off. Sorry to be a pain, would i be risking a dangerous situation if i fitted a check valve in the cold feed from cistern to cylinder to prevent flow back up to cistern.

Answered my own question i think, if i fit check valve i will get overflow up through vent pipe i take it.

 

[HarrogateGas]

No you will just get no hot water, non return valves need a pressure (either mains or pumped) to open, gravity alone from your tank will not let water through down the cold feed to cylinder.

 

[Dboing]

Thanks harrogategas, good learning curve this but at a bad time xmas and all that. Fitted 2 new Ball cocks now in heating expansion tank and domestic cistern, gonna run the full system for an hour at a time to give domestic hot and heating then turn off before i get overflow occuring due to cylinder coil passing into cylinder can anyone see any dangers with that.

 

[HarrogateGas]

If you have an immersion heater than a quick fix would be to capp off the cylinder flow and returns and use the immersion heater for dhw.

 

[Dboing]

chears HG,
so easy when your not as dumb as me. At the moment with the heating pump running on 2 or 3 the cistern is slowly filling up but with the pump set to 1 the water level in the cistern seems to be stable, down side some radiators are only getting warm but system has only been running for 30mins.
Thank you all for your time and consideration, hope this is goodbye and a merry xmas to all but have a funny feeling that i maybe back, lets hope it is to help out someone else next time.