c/h pump flow rate problem

anymouse

Hi,

new member here....

I'm having a problem with my c/heating system which hopefully someone here can shed some light on..

The central heating in my house was originally provided by a solid fuel range with back boiler which was in the kitchen. When refitting the kitchen, I ripped out the range and extended the 2 pipes outside in order to fit an outdoor oil boiler instead. The circulating pump on the original system was located in the hot press on the return leg going back to the boiler. Fitted the boiler last month and had the pump on a switch, heating all worked perfectly, however, I wanted to put the pump in beside the boiler so I could easily wire it to the same timer supplying the boiler. So, fitted a new pump the other day, refilled system, bled etc, no problems. Started up the boiler and pump and water started coming out of the fill and expansion vent pipe and overflowing. I had a chat with the guys at the builders merchants but they were a bit non plussed, reckoned maybe an air lock some where, but the systems seems to bleed really easily, so I'm kinda doubting this theory. I thought it may be the new pump was too strong and flowing the water in the system too fast, so i swapped the pump with the old pump which still works perfectly, but have the same problem, even setting the pump on the lowest speed setting, it still overflows from the vent pipe slightly. I'm wondering if it's because i fitted the new pump on the output leg of the system, i.a coming from the boiler whereas the old pump was on the return leg and having to "push" the water through the heat exchanger, which i assume would slow the flow down a bit. Should I have fitted the new pump on the return pipe just before the boiler? I just need a bit of advice before I go having to replumb everything at the boiler for that set up, only to find that it may just be the same...

Thanks in advance folks.

DonkeyStyle \o/

Sounds like you made a complete balls of it alright...


Oh and welcome to boards.ie by the way.

anymouse

Thanks for the welcome and the useful comment. I wouldn't say that I made a complete balls of it. If it needs to go on the other pipe, it's easily sorted, and if that doesn't work, the old pump can always go back on in the original position, it's just harder for me to wire the electrical side of things into the timer, due to the distance.

JamesM

Usually the pump is on the return. When it is on the flow you can have problems, like sucking in air from a weak safety valve or automatic air vent etc. Did you close the rad valves when draining and have you opened them again ?

A lot depends on your system, but having the pump on the return should certainly lessen your problem.
Jim.

anymouse

Thanks James.... that's exactly what I had hoped to hear.
All rad valves were open when draining.

There are both a PRV and auto air vent fitted plus I think the vent pipe is probably fairly close to the output side of the pump maybe making it like effectively turning on a pump on a negative head system and opening a tap??

I'll move it to the return leg and keep fingers crossed!!

Calibos

We had a back boiler replaced by a gas boiler which went in an upstairs bathroom years ago in my parents house. New pump was added to pipes in the hot press and I remember water coming out of the overflow. Plumber came back and realised he had made a silly mistake and laughed. Now that the boiler and pump were upstairs the water needed to be pumped downstairs. He had mounted the pump pumping in the wrong direction. Refitting it properly resolved the problem. Dunno if this info helps