Warm Header Tank

A few months back we took out our back boiler and put in a stove which I must say has been a great success. Before putting it in I discovered we had a closed loop heating system (oil boiler and back boiler) with no header tank. Anyway the plumber putting in the knew this and told me (as well as others) that it shouldn't be a closed loop and he'd have to put in the header. He did the job and all was fine until I noticed some air in the rads that I had to bleed. He came back a number of times and tried different things to remedy this but nothing worked until he put another pipe into the header tank - I'm not sure for what. Anyway - no air in rads now. However recently I've been in the attic a few times and noticed some floor boards damp, I went looking for a roof problem and found the inside felt damp over a fair big area. I just happened to look at the header and felt it warm and when I put my hand in the water was maybe 30dC - you could wash up in it. Is this normal for the header to be warm and could it be causing condensation and that's what I felt? Is this a problem?

That is not normal, your system is back filling, the header tank should only have a small amount of water in it, ensure that the overflow pipe from the header allows water if it overfills to escape to the outside, it may be that this is not happening hence the damp floorboards etc, you need to get a plumber in, don't delay, another issue with the backfilling is that air is making it's way through your rads, this causes rust inside your radiators thereby reducing servicable life.

Thanks for the replies guys. There is no air now in the system and should the header tank be heating up? What should I ask the plumber to do?

Forgot to add that he did put in an aniti rust additive when filling up the system, would this help?

Are you turning off radiators? What could be happening is when you turn off radiators the circulation pump is still running at the same speed creating the same "head" which is getting pushed up the expansion pipe and into the header tank. Check what speed the pump is on and reduce it, they normally are 3 speed pumps and most plumbers set them to 3. Try setting it to 2 and see what happens. It could also be happening if you have zones being switched out when rooms reach their set temperature.

Thanks Caff. No not turning off rads at all. The house is not zoned at all. But just to get back to 1 of my basic questions - Should the header tank get warm? And is this causing my condensation?

149oaks said:

Should the header tank get warm? And is this causing my condensation?

Click to expand...

No, it should not get warm and may well be helping to cause condensation.

Thanks Sparkrite

SparkRite said:

No, it should not get warm and may well be helping to cause condensation.

Click to expand...

This is correct.
The usual suspect is either the open safety vent pipe or the feed & expansion pipe position in relation to the circulating pump. When the system is on, is there water coming out of the osvp. This is the hockey stick shaped open ended pipe curved over the top of the f & e tank. If so, the system is pitching & the tank is acting like a radiator. This will eventually destroy your system.
If not, then the pump is probably pumping into the tank through the f & e pipe. It should be located on the negative side of the pump.

If you do have or wish to have solid fuel with a back boiler, then you could eliminate the f & e tank altogether & pressurise the heating system. You will have a far more efficient heating system with far less issues overall. You will have to of course, install a few more components to do so.

Thanks Shane. This is all getting a bit beyond me but also scaring me.
But 1 thing was that before the stove went in the system was pressurised and I was told by a few plumbers that this wasn't safe, it would have to be changed and a header tank put in as part of the job.
I know the plumber put a pipe into water in the tank that would suck water into the system in case it was sucking air in if it wasn't in the water.
I really don't know what's happening at this stage.

Is there a pipestat on the system to automatically switch on the circulation pump? Try turning it down a few degrees, maybe there's some boiling in the stove which is forcing water up into the header tank.

Shane007 said:

This is correct.
The usual suspect is either the open safety vent pipe or the feed & expansion pipe position in relation to the circulating pump. When the system is on, is there water coming out of the osvp. This is the hockey stick shaped open ended pipe curved over the top of the f & e tank. If so, the system is pitching & the tank is acting like a radiator. This will eventually destroy your system.
If not, then the pump is probably pumping into the tank through the f & e pipe. It should be located on the negative side of the pump.

If you do have or wish to have solid fuel with a back boiler, then you could eliminate the f & e tank altogether & pressurise the heating system. You will have a far more efficient heating system with far less issues overall. You will have to of course, install a few more components to do so.

Click to expand...

How is this done? I thought it was forbidden to have an uncontrollable heat source in a sealed system.

Apologies I misread the OP! I only read removed the back boiler & did not read the replacement with the stove.
No, you cannot have a solid fuel system pressurised.
Now that there are two sources, I wonder did the installer fit 2 feeds. This would also cause the tank to heat as it creates a circuit. The system should have 2 vents but only 1 feed/expansion.

Thanks guys. Plenty of food for thought and I need to get the plumber back. Do ye mind if I show him your comments? What specifically should I ask him to do?

By all means show him my comments anyway. It's hard to know what to say to him. The only way hot water is getting up to the expansion tank is via the expansion pipe (swan neck shaped pipe). This should not be happening during normal operation. Maybe rising the pipe higher over the tank might be all it needs or the pump speed to be turned down. It's really difficult to help without seeing the setup. Are you in a bungalow or two storey house?

I have similar problem with attic tank heating. Existing common heating loop for gas boiler was divided to have one zone for heating and one for hot water recently. Noticed today that hot water is entering the tank in attic via the vent pipe. So I assume based on the above that this should not happen. Two queries. 1. In a system which is split to 2 zones, should there be 2 vent pipes to attic? 2. As this is conventional system, is there a chance that system cannot be set for heating rads only I.e. heat water only or heat water and rads but not heat rads only

If the issue is only happening since the zoning works have been implemented, then the installer has not given consideration to the location of the connection point of the feed & expansion pipe to the system. Basically, what is happening is the zone valves when closed are blocking access to the f & e pipe.
To test, if you turn on all circuits at the same time, does the system pitch water through the vent pipe. If not, the issue is definitely as I described.
In the system you have described there should only be one vent pipe.