Hot water boiling over

[APE]

Hi

I have recently had my boiler moved, all well and good. But it seems that ever since I had it moved, whenever JUST the hot water is on it seems to "boil over" out of the expansion pipe and into the header tank, then subsiquently over-flow all over my drive way. When the CH is on at the same time this doesn't seem to happen. It is also worth mentioning at this point that I also had an additional zone valve fitted when the boiler was moved to independantly control the HW (before, the HW always had to be on for the CH to work).
Also, possibly worth mentioning: I have some DIY plumbing knowledge, but I am no plumber by any stretch of the imagination, but i was under the impression that you had to have at least one radiator on the same "circuit" as your heating coil and i don't. Is this right or am i just talking nonsence?!!!!

Any suggestions would be much appreciated.

Cheers

 

[methaneman75]

sounds like the expansion pipe has not been moved with the boiler/pump and is probably pumping over all the time. check to see if the ex pipe is before or after ther pump. Also, constant hot water in header tank could soften /loosen plastic fitting on tank so beware of leaks if this does not get fixed.

 

[methaneman75]

also, check that there is a bypass fitted between flow and return before the zone valves, this is just an interconnecting pipe between the pipes to allow the water to circulate when controls have been satisfied

 

[muggles]

Ditto, and no, in general there should not be a radiator on your DHW circuit

 

[APE]

Thanks methaneman75, the boiler was only moved about 2 metres from the middle of the kitchen wall to a cupboard in the corner. And from what I can tell, the expansion pipe is before the pump (I presume by before you mean on the return pipe).
I have attached a quick rough sketch of the plumbing layout in our house, is it strange that the zone valve for the CH is on the return leg, yet the zone valve for the HW is on the flow leg, or is this quite normal? I also notice that the pipes that feed the HW coil are the wrong way round according to the diagram on the side of the cylinder (Although the only way i could check was to turn the HW on and see which got hot first, and they got hot v. quick, so i hope i'm right), is this detrimental to the system?

Also thanks for clearing the radiator query up muggles.

HW_CH Scematic

• APE
• 22 Nov 2008
• 2

 

[simond]

You really shouldn't have gone to all that trouble.

 

[APE]

You really shouldn't have gone to all that trouble.

Yeah ~I know, it took me hours!!

But have you got any advice for me????

 

[JPC]

if i told you your arrows are pointing the wrong way..ie flow goes into the top of the cylinder coil and comes out the bottom...did you fit the zone valve ?...does it open when it should ?...back to front ?

 

[snb]

flow could be in the bottom of cylinder coil. It is the correct way to plumb fully pumped cylinders. It heats the system up quicker. All unvented systems are plumbed this way and it is the only way to achieve the reheat times.

( i found this out when i did my unvented course)

That being said most you come across will be the other way people just followed the gravity principle.

 

[APE]

also, check that there is a bypass fitted between flow and return before the zone valves, this is just an interconnecting pipe between the pipes to allow the water to circulate when controls have been satisfied

What do you mean by this interconnecting pipe, and where should it go?

Also, the drawing is the way the cylinder is plumbed, is it right or wrong? I have double checked the pipes when I first put the HW on and the bottom pipe definitely gets hot first.

 

[JPC]

check this link

[/url]http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm

 

[Goldspoon]

http://content.honeywell.com/uk/homes/FAQ/@Semi-gravity conversion.pdf

http://www.iphe.org.uk/student/controls.pdf