Boiler thermostat setting

Hi All,

I've noticed that if I have the boiler thermostat turned up too high, (over 4 on a 1 to 6 scale) I seem to get an overflow from an expansion pipe that runs outside. Also, I'm sure I have to bleed one of the rads far more frequently as well. Once a week. Any idea what might be the issue?
It's a normal old style system with a non-condensing boiler.

Thanks.

Sounds like the system may be pumping over.....

The pump may be sluggish or set incorrectly and not allowing the boiler to get rid of the heat quickly enough.... Your appliance should be able to work on the full 1-6 scale without pumping over.....

This info is very general however, and I would need more info on system design to give an accurate answer....

Martin

PS; pumping over is basically where water is expelled from the heating circuit back into the header tank, via the open vent....

You'll know if this is happening by having a look in the header tank... If the water is hot/warm... this suggests it's pumping over....

Martin

Thanks Martin,

This make more sense now as I've been told in the past that our pump may be on it's may out. It has three settings and is on the top setting. I stops pumping on the lower speeds.
This isn't overflowing into the header tank, it's going outside the house. This is a bit of a concern now as this is hot water and some one could be standing under it.

If the pump only works on the high setting then there's a fault with it (or in the circuit where the pump setting dial is on the side of it). Fix that first.

Then work out where the feed pipe connects to the circuit, and where the expansion pipe connects. They should be (from memory) 6 inches apart on an unrestricted section of the circuit, before the pump, feed first, then expansion. If they're connected either side of a cylinder (as mine used to be!) then the pump sends the water through the expansion pipe and back down the feed instead of around the cylinder / radiators. That, together with the high pump speed (more "violent" flow) will cause it to overflow. Also note that having hot water in the feed tank is dangerous. Plastic tanks can melt and dump their hot contents all over your ceiling. They're designed for cold water only.

Hi,

I should have clarified.... When the water pumps back into the header tank it raises the water level, which will then case it to run out of the overflow...... This water would be hot as a result of the pumping over....

It really sounds to me as though the pump isn't running properly (sluggish) as opposed to it running to quickly as suggested in the prev post....

I see this as a symptom of the pump running poorly as opposed to the setting being too high.... The fact that it has been set at 3 in the first place suggests there was a similar problem in the past which someone tried to correct by increasing the pump speed (in an effort to have the heat taken from the boiler more quickly). While there may be an issue regarding pipework, I don't think this is your main problem.... What type of pump is it....?? Myson? Grundfos? Wilo??? euramo gold????

Martin

Sounds like the system may be pumping over.....

Click to expand...

Why does it not pump over when the systems colder then?

To the Op's original post..... Which tank is higher in the loft.....the CWS or the Header tank?

Faulty boiler Stat possibly? Im guessing it boiling with the stat turned up too high.

Flooze.

The clue's in the question....

Because the lower the stat is, the lower the flow temp will be..... Therefore the pump will be able to get rid of the heat much more easily.... ie: if the stat is at 1 the pump will deal with this substantially lower temp.... if set at 6, the pump may not get rid of the heat quickly enough from the h/e, allowing it to boil, hence pumping over..... This would provide almost identical symptoms to that of a faulty boiler stat as you suggested.....

....... While this is not the only cause of pumping over (over sized pump, incorrectly sited pump, blockage in cold feed), based on the symptoms it is quite likely in my view.....

Martin