Hot water getting into header tank

[neilo]

Hello - I have hot water getting into my CH header tank through the vent pipe

I have looked at similar threads here and done everything they suggested ie turning down the pump (it is on #1 setting , raised the header pipe it is 1.5 m higher now ) however i still get hot water running into the header tank
I have drained the system down and the header water level dopped and filled up again as it should which would suggest no blockage - so now I am stumped - would appreciate any assistance here - help!!

thanks Neil

 

[buffy27]

Hello - I have hot water getting into my CH header tank through the vent pipe

I have looked at similar threads here and done everything they suggested ie turning down the pump (it is on #1 setting , raised the header pipe it is 1.5 m higher now ) however i still get hot water running into the header tank
I have drained the system down and the header water level dopped and filled up again as it should which would suggest no blockage - so now I am stumped - would appreciate any assistance here - help!!

thanks Neil

is this a new problem with an existing system , a problem because of work done or is this a new installation/new build.?
another possibility may be a hole in the coil of the cylinder,where the dhw and heating waters are mixing.
how hot is the water getting.?

is it only when the heating is going through the coil.?
is the water coming up the over flow pipe or back up the top up?

 

[sonray ltd]

sludged system.
faulty boiler stat. whats the boiler stat set to ?

faulty coil will release water up the feed pipe not the vent pipe.

 

[dam]

Its sounds to me like your pump is in the wrong place!

 

[neilo]

Hello Guys - Thanks for the responses - I am grateful here are my answers :-

Firstly the system is 15 years old - 1 year ago the pump went and was replaced with identical Grundfos pump (which appears to be working fine)

This week I replaced my switchmaster mid position valve (as it had stopped working auutomatically)with a Honeywell V4073 BUT the water in the header tank was already hot when we went to drain the system so I dont believe it is the new valve (which again appears to work fine).

I happens on all boiler settings but stops after 10 mins on heating only with pump set on #1 - (set to #2 it is constant).
It is constant with both CH & Hot water . (I havent tried HW only yet)

It only comes up the overflow (open vent) pipe into the header tank

Boiler stat is set at 3 - 4.

It does have air separator but as I said earlier the intial drain of the system went OK and emptied the header tank which sort of indicates no blockage -doesnt it??

Once again really grateful for all the help

 

[justlead1]

Hi. Have you tried extending the vent pipe, That is to say the point at which it bends through 180 degrees extended up 18" higher. Good Luck

 

[sonray ltd]

if the systems been ok for 15 yrs and you haven't had any pipework alterations no reason it shouldn't run for another 15 yrs.

you say you have checked the boiler stat is working correctly.

also you have not ruled out a sludged system just cause it drain and fills ok it can still be sludged.

 

[neilo]

The 3 port valve is correct A to heating and B to cylinder.

I have already raised the header pipe by 1.5 M and the water still gets up there so there must be quite a bit of expansion or back pressure .

Could sludge really be the cause even if the system appeared to drain down and there are no real pointers to indicate sludge ??

 

[fatoftheland]

Was the pump taken out whilst the 3 port valve was fitted and put back to front, look at the arrow on the pump, and while you are there, check both pump valves are open, and I mean properly check, there is a bit of slack on the valves and every apprentice i ask to check em says they are open

 

[sonray ltd]

BUT the water in the header tank was already hot when we went to drain the system

you have stated the problem was already their before any work was carried out.
you say the boiler stat is working.
your valve is working ok and fitted after fault.
pump speed low and circulating the right way. (which you would soon know if it wasn't)

we nned abit more info on how the boiler performs when running.

does it cycle alot ?
does it reach room temp quick ?
does all rads heat fully & evenly ?

 

[justlead1]

Hi. Have you looked in the loft for the last 15 years? To push water up 1.5M it must be the relationship of cold feed and vent. Put a cork in the cold feed connection in cistern (temporary) monitor results. Reroute cold feed connection so as not under suction from pump. Good luck

 

[neilo]

Ok - here goes round Three

Pump definitely right way round arrow pointing down in direction of flow.

Boiler appears to cycle OK (though what would be considered normal??)

it takes about 30 mins to an hour for house to get up to temp.

All rads are warming up but longest away tends to take longer now I have dropped the pump speed but hey do all heat up .

When you say cork the cold feed I assume you mean the gravity feed back down from the header tank - at the moiment this is just cycling the hot water that comes out of the vent - the mains feed never needs to operate as the water level is constsnt (except loss due to steam)

Once again thanks guys - see it as a challenge

 

[paulhield]

I have had this problem and fixed it. My cold water feed and vent pipes were close to each other between the boiler and pump. The vent was upstream of the feed. When the system was at maximum flow, surprsingly sufficient pressure drop occured between the vent and the feed to force water up the vent and into the header tank. It required that both the motor valves for the CH and hot water were open.... this maximised the flow and hence the pressure difference between the vent and feed.

The solution is to always make sure the vent is downstream of the feed. That way the vent pressure will be lower than the feed.

Perhaps someone could tell me why we need a separate vent anyway, since any excess water or gas can go back up the feed pipe. Think about it, the vent and feed are two parallel pipes side by side. Both have nominally the same head of water above them, so why would excess fluid choose one over the other, surely the vent pipe is redundant? Eliminating the redundant vent pipe would eliminate the header tank recirculation problem.

 

[help me!]

I have this exact same problem . The feed from header tank was initially totally blocked. Once this was cleared, water flowed up the vent pipe, into the header tank and back down the feed. Hot water from the taps is normal temp, pump is running correct way on lowest setting. I have fitted new TRV's to the rads, a new pump and 2 new 2-port motorised valves. The heated water flows thro the header tank when the boiler is heating hot water, central heating or both together. I have opened up the regulating valves on all rads to try and reduce the back pressure but it didn't make any noticable difference. The vent pipe is around 4 foot vertically, I read on another thread that increasing this height can help? I also read that the vent should be downstream of the feed? My vent is 4" upstream of the feed. My boiler is cycling fairly quickly, not sure eif this of any relevance.
Any advice would be greatly appreciated!
Thanks
Lee

 

[oldie]

Hi Neilo, meny years ago I had exactly the same problem , you haven't mentioned anything about your hot water storage,is it a cylinder were the water is heated by a internal coil . Ours was originaly a conversion that screwed into the immersion heater boss, if I remember correctly, it had three sort of flattened tubes that ended in a soldiered disc type of boss/plug.this over time corroded and fell to the bottom of the cylinder , this allowed the circulating hot water to pressureize the hot water cylinder that, then vented into the expansion tank and the water was Bl--dy hot ( steaming). So as Buffy 22 has already suggested you could have a hole in the cylinders internal coil that is allowing the heated water from your boiler to leak into the hot water cylinder and eventually to vent into your expansion tank.
oldie