central heating

Post by **jtd.75** » Sat Jul 11, 2009 8:06 pm

I know its not car orientated, but our forum has more expertise than i know of

my daughters central heating header tank (thats the smaller one of the two) over-flows when she puts on the domestic hot water to heat and stops when she turns it off again. the water is comming back up the feed pipe to the boiler as if there is a back pressure, the ball cock a doodle diddley and vent pipe are not the culprits and the coil inside the hot water cylinder has not perferated. The C/H system is oiled fired open vent and has 2 pumps, 1 for domestic hot water and 1 for central heating with no motorised valves only thermostat rad valvs (trv's) and a cylinder stat that controls the hot water pump. there is also a heat sink (2 rads off the DHW) with no trv's on them. After the dhw as been on for a while the water in the header tank is hot. Has anyone got any ideas on what the cause is.

Post by **alex_holden** » Sat Jul 11, 2009 9:02 pm

Does it start overflowing immediately after you switch it on, or only after the boiler has had time to get hot?

Post by **Longdog** » Sat Jul 11, 2009 10:11 pm

You asked at the right place as I am a heating Engineer.It sounds like a blockage betwwen the open vent and cold feed.This area generally closes up anular fashion until you end up with a 10mm hole.
As this is the only point where air can be drawn into the system.
I assume water issues from the open vent into the header tank.
This is because the pipe cannot carry the volume of pumped water.
If you cut into the pipes in the area of the junction between cold feed and open vent you should be able to rod pipes.
2 pumps on a system is unorthodox to say the least.
I hope this helps, by the way drain system below pipes being cut first.

Post by **alanworland** » Sat Jul 11, 2009 10:26 pm

This is one brilliant forum!

Post by **bmcecosse** » Sat Jul 11, 2009 11:36 pm

You say the coil inside has not perforated - but it sounds very much as if that is exactly what has happened! How do you know for sure it's not perforated ? I agree with longdog - two pumps is most unusual arrangement!

linearaudio · Post by **linearaudio** » Sun Jul 12, 2009 5:51 am

Can't say I agree about the 2 pumps- In my Bungalow and my Mums, and also daughters Bungalows, both circuits are pumped, I understood it was to compensate for lack of head to hot water tank (though it's twenty years since I seriously studied domestic plumbing when I couldn't get our "cowboy" system to function and ended up re-designing it

)

By the way longdog- it's great to see your use of "issue" in one of its proper forms, rather than the trendy use of the word to cover problem, matter etc. Getting to be as mis-used as "literally"

Post by **Longdog** » Sun Jul 12, 2009 8:29 am

A perforated coil in the cylinder will cause water to migrate from the domestic hot water tank to the header tank through the pinhole.Water tries to find its way to level which means your o/flow from the header tank will be constantly dripping.
In a bungalow two pumps is a way of getting round the lack of "gravity" head so in some instances it is fitted to compensate, but is not ideal.
If you look at the open vent/cold feed arrangement I suspect they may be coming off the primaries into the cylinder in which case you could try a flushing agent to shift the constriction in the pipework.Best product for this is Fernox Superfloc.Leave in for 2 weeks, drain, flush and add an inhibitor.
If your pipes are conjoined in the area of the pump within 6" this is a close coupled system and although the modern method, blockages will be concentrated here.
As a final note if no overflows are dripping don't go to the expense of a new cylinder.

Any probs I will be happy to help, Andy.

Post by **jtd.75** » Sun Jul 12, 2009 11:11 am

Hi LD, the bungalow is 20 years old and at 1 time it only had a coal fire with a back boiler which heated the dhw and it was pumped via a grunfos pump in the loft space to the hw cylinder. Like i said in the beginning the water is not comming from either the vent pipe or the ball cock a doodle diddley, it is comming back up the pipe that keeps the water in the boiler system topped up and only when dhw selector switch is operated and thats after the boiler has been runnig for about 10 mins or so as soon as the water gets hot. I drained the system down last september to fit trv's and do some decorating befor she moved in. everything was ok untill a couple of weeks ago when she stopped using the central heating. Once she runs the bath the water stops comming out of the over flow (from the feed and exspansion tank). If the coil had gone would'nt the water from the hot water taps be discoloured!!. Once she deselects hots on the programer all is returned to normal. I forgot to mention that the pump for the ch is also in the loft about 10 feet from the dhw pump. and the oil fired boiler is in the garage next to the house

Post by **jtd.75** » Sun Jul 12, 2009 1:23 pm

Hi Alex, only after the water heats up and no its not vent pipe i/e steam turning to water

its comming back up the pipe from the feed and expansion pipe, originally the bungalow only had a coal fire with a back boiler and a pump to pump the dhw around the bungalow. And about 8 years ago the chap had the fire taken out and in the garage he had fitted a oil fired boiler for the c/h and the original h/w system looped into the boiler, comming out of the top of the boiler (dhw flow & return) the is a pipe going to 2 rads as if to act as a heat sink!!.
Jimmy

Post by **crossword** » Sun Jul 12, 2009 5:00 pm

I'm not a heating engineer , although I have installed a few systems . This sounds like the C/H system I inherited in this house 20 years ago . It may be that the pump is fitted in the return to the boiler but before the feed from the expansion tank . The slight resistance in the boiler may make for increased pressure in the feed pipe , with a rise in the level in the expansion tank . In my case this overflowed but when it was off the level would drop & be refilled by the ball valve . Mine was also an upgraded gravity system .

Hope this helps . Regards Andy.

Post by **beechford** » Mon Jul 13, 2009 10:55 am

if you closed down the system to decorate ,have you since then Bled the air out of the system. Our old house in Tamworth had to be bled at the end of summer every year. starting aty the closest to heat source finishing at the furthest away and as long as we kept a fire going that was it .hope its of some help.

Post by **jtd.75** » Mon Jul 13, 2009 1:30 pm

First Crossword yes I think what you have described is the same set up as whats in my daughters bungalow, how did you solve the problem. Next Beechford reply yes I did bleed all of the system and correct procedure was followed.

Post by **simmitc** » Mon Jul 13, 2009 1:55 pm

I'll bow to LDs greater experience, but one other thought: Is the pump fitted with a variable speed/head control? I've seen some where the pump is set too fast which pressurises the system and sends water up the pipe. Setting a lower speed solves the problem.

Post by **jtd.75** » Mon Jul 13, 2009 2:08 pm

HI thanks for your imput, that was the first thing or at least one of them that I thought might be happening at the beginning and still might be the cause, there are 3 setting on the pump and its set at the lowest (1 ) assuming that 1 is the lowest. I am goint to ring one of of our colleges that put forward a reply earlier on this topic later to night.

Post by **jtd.75** » Mon Jul 13, 2009 2:15 pm

Regardless of what the out come will be to my dellemma there is one thing that I can say about our forum and that is how brilliant it is. No matter what you ask some one will always try to come up with a sollution to one problems

. Membership money well spent, thanks all

Post by **crossword** » Mon Jul 13, 2009 4:59 pm

jtd,
Turning the pump speed down may help as simmitc suggests . To further paint a picture , the installation was like a ships boiler house with many pipes going up & down walls then through them to rads the other side . I decided the only sensible thing was to take it all out & start again with new . This was decided on a day in summer when hot water was issuing from the overflow onto the driveway during a hosepipe ban !

Good luck with it Andy

Post by **jtd.75** » Mon Jul 13, 2009 5:42 pm

thanks Andy