Water coming out of vent pipe into central heating F&E t

[coldmonkey]

Hello,

I've what I imagine is a standard open-vented central heating system with an indirectly heated hot water cylinder. The boiler is fairly old but apparently is well made (Ideal classic).

I've recently had three new radiators fitted as well as a new 3 speed Grundfos pump (pump was fitted a few weeks before radiators). The system was also treated to a chemical flush for one week (which is how long the new radiators have been fitted).

I was up in the loft earlier and I happened to be up there when the pump shut off and I noticed that water came out of the vent pipe (not forcefully, but the trickle lasted for about 1 minute) into the F&E tank. I've reduced my pump speed to 1 and that seems to have reduced the amount of water coming up the vent pipe to a small 5 second trickle, but it still happens without fail everytime the pump stops (you can feel the hot water travel up the pipe when it stops and then it gets cold again when the pump restarts.

I'm now at a loss as to how to fix this and I'm probably going to be stuck getting anyone out soon at this time of year so I'd appreciate any ideas. Apologies for the lengthy post, I'm trying to give as full a picture as possible.

Thanks.

 

[doitall]

It's a surge when the pump stops, and nothing to worry about.

The cure would be to fit a large pipe as an shock arrestor in the vent pipe, raising the vent pipe and or, the header tank may also stop the problem

I would gather you have a low head.

 

[ChrisR]

It's definitely something to fix. It causes oxgenation of the water, as in a fountain, which causes corrosion in the system. Eventually it kills boilers.
Taking the vent pipe in a higher vertical loop is usually the simplest solution.

 

[coldmonkey]

It's a surge when the pump stops, and nothing to worry about.

The cure would be to fit a large pipe as an shock arrestor in the vent pipe, raising the vent pipe and or, the header tank may also stop the problem

I would gather you have a low head.

Thanks for the response.

I'm I right to have slowed the pump down? This seems to have reduced the amount that comes out or does that not matter? Yes there isn't much head.

 

[ChrisR]

That depends whether you're left with enough flow to heat all the rads!.

Try bleeding all the rads. Trapped air can act as a "spring" and make the water bounce about more.

 

[coldmonkey]

That depends whether you're left with enough flow to heat all the rads!.

Try bleeding all the rads. Trapped air can act as a "spring" and make the water bounce about more.

I've already done this, since I was advised that after the system was refilled, I may need to bleed a few times. Having said that, I've not really found much water coming out. I will get the vent pipe replaced (I need to anyway as it leaks a bit).

Whilst I'm at it, have you got an opinion as to whether changing over to a combi boiler is a good idea? I ask because I've got a fairly old system that has already leaked under my bathroom floor (nightmare story) and I've had other bits of pipework replaced that have had obvious corrosion as they've been discovered and I'm thinking of getting the whole house re-piped etc. If I stay with the Open vented system, I will have to replace a poor performing old hot water cylinder that takes about 1.5 hours to reheat, which is a real pain with a pumped shower. I'm quite attracted to the idea of getting the water out of my loft and having a system that I can tell is leaking (since it is sealed and you can see a pressure drop when sealed systems leak). I have a traditional 3 1960s bed house with 1 bathroom

 

[coldmonkey]

That depends whether you're left with enough flow to heat all the rads!.

Try bleeding all the rads. Trapped air can act as a "spring" and make the water bounce about more.

I've already done this, since I was advised that after the system was refilled, I may need to bleed a few times. Having said that, I've not really found much water coming out. I will get the vent pipe replaced (I need to anyway as it leaks a bit).

Whilst I'm at it, have you got an opinion as to whether changing over to a combi boiler is a good idea? I ask because I've got a fairly old system that has already leaked under my bathroom floor (nightmare story) and I've had other bits of pipework replaced that have had obvious corrosion as they've been discovered and I'm thinking of getting the whole house re-piped etc. If I stay with the Open vented system, I will have to replace a poor performing old hot water cylinder that takes about 1.5 hours to reheat, which is a real pain with a pumped shower. I'm quite attracted to the idea of getting the water out of my loft and having a system that I can tell is leaking (since it is sealed and you can see a pressure drop when sealed systems leak). I have a traditional 3 1960s bed house with 1 bathroom

Re: bleeding - I meant to say not much air coming out

 

[doitall]

Changing over to a sealed system would be a good way to go, but, you will probably have to change the lot, pipes and radiators, by the sounds of it.

 

[Blooflame]

Your problem is either system design or more likely the cold feed is blocking up.