Hot water circ. pump overflows hot water into F&E cister

[charding370]

My C/ Heating system orginally had one pump and gravity fed hot water heating the hot cylinder upstairs. About 15 yrs ago we had the boiler moved into the utility room and the hot water didn't get hot as it couldnt gravity feed round the added pipe bends from the utility room into the kitchen before they go up into the first floor and into the hot tank. Its all in 28mm pipe to the hot tank. So the guy who moved the boiler added the pump on the return side and its worked fine ever since.

Recently the pump failed and was replaced with a Primeflow CP 5m heating circulation pump, and ever since whenever the pump is switched on (when hot or cold) it overflows up the expansion pipe into the loft F&E cistern. When it reaches a certain level it doen't get any higher and never overflows the F&E tank as it settles a few inches below the overflow pipe.

This is hot water going into the F&E cistern and wasting energy as well as getting it hot and making condensation in the loft.

Do you think the new pump is too powerful a head rating at 5m, or maybe there is a blockage in the pipework but that seems doubtful as the water in the hot tank gets hot quickly enough. I have added X400 into the F&E tank but not drained off and refilled system yet as I am convinced this is the problem.

Can you buy a low rating circ. pump and if so do you think this will cure this problem?

 

[simond]

Recently the pump failed and was replaced with a Primeflow CP 5m heating circulation pump, and ever since whenever the pump is switched on (when hot or cold) it overflows up the expansion pipe into the loft F&E cistern. When it reaches a certain level it doen't get any higher and never overflows the F&E tank as it settles a few inches below the overflow pipe.

This is hot water going into the F&E cistern and wasting energy as well as getting it hot and making condensation in the loft.

The original pump may have had three speed settings, and if so may have been set to the lowest.

The CP pump is a budget unit often fitted by insurance companies, you can buy one from certain outlets and get change from a £20.

Fundamentally, the system design sounds wrong and was boidged to start with when the boiler was moved.

Your biggest problem is not heat loss or condensation, it is the massive corrosion that your system is now experiencing from the oxygenated water.

 

[charding370]

Now your got me worried, I suppose this is circulating round the system from the F&E tank.
I was charged 55 pds for the pump by a reputable local company called Paine Manwaring who claim to be heating engineers but it was needed in a hurry as the old one failed so no hot water. It IS on the lowest setting.
Would a lower rating pump not fix the problem?

 

[Agile]

£55 to supply and fit a new pump is way too low to expect an professional service.

The pump may have a speed selector and you can mostly close the pump valve as required.

Once the pumpover is cured you system will need power flushing or properly cleaning.

Pumping over will start to pin hole rads within weeks and to sludge up the rads even sooner! Its very stupid to even use it in that condition.

Tony

 

[charding370]

It was 55 for the pump plus fitting. I have been told elsewhere to partially close the shut off valve on the pumping side to reduce the output of the CP pump. For all I know it could have been partially closed with the old pump when it was fitted.

I didn't know about this oxygenating thing until getting on this forum.
The new pump was installed before Christmas and I only noticed there were signs of condensation when I went in the loft in January and realised the water was warm in the F&E tank. Its on 1.5 hrs in the AM and PM to heat the water.
I cleaned ou the F&E tankd and added 2 x 1 ltres bottles of X400 last week incase there was a blockage and aim to draining the system soon.
I will post again after I have turned down the outlet valve and let you know if this fixes the over flowing problem.

 

[picasso]

I would also make sure the pump is pushing water in the same direction as before, they may have put it in the facing the wrong way.

 

[charding370]

No, the pump is pushing water towards the boiler on the return side and that is the same direction as before.
I have now throttled the output valve from the pump until water stopped coming out of the overflow. This was when the bolier was off. Suppose I will have to turn it down a bit more when the boiler is on. Will this damage the pump as it is working harder or is it just the flow through the pipes is less?

 

[Agile]

The pump is working less when you reduce the flow!

Is there also a speed selector?

Tony

 

[charding370]

The pump is working less when you reduce the flow!

Is there also a speed selector?

Tony

I meant, as it is working against a restricted pipe area ahead of it.
Anyway the overflow has stopped and I with the heating on the expansion pipe up to the loft above the T piece into the hot tank no longer gets hot higher than a foot or so.

The speed selector is on "1.

Should I drain and flush system in the next few weeks to get rid of oxygenated water, in which case put in some X800 as well and afterwards add X100 inhibitor, or leave it until such time as I can get a heating engineer to modify the hot water system to a more satisfactory design?

 

[simond]

I would leave things as they are, adding some inhibitor ieX100 will help reduce corrosion.

If nothing else untoward happens (eg it doesn't pump over) leave it until you change the boiler. Assuming you were content with the way it was operating before the pump was changed out.

 

[charding370]

If I had the system upgraded what mods would be recommended to stop the boiler short cycling?
I dont want the expense of a complete replumb for separate hot water or heating.
I have a motorised valve on the flow side of the hot cylinder but its never been wired in as I didnt know how to wire it up to control the boiler. So I added a cylinder stat to control the hot water circ. pump but it doesn't shut down the boiler.
Some one mentioned somne kind of interlock to stop the boiler firing when both stats are "off".