Gravity HW backwards

[r.bob]

Boiler idle over summer. Drained, rad valves added (by me), boiler serviced and re-set (by Corgi chap). This is an old pumped CH, gravity HW system.

After intitially having difficulty getting the HW to gravitate properly (prob air block) it now prefers to travel the wrong way, leaving the boiler via the return connection, eventually travelling upwards through the tank and then struggling back via the outlet connection.

This does not work very well! Any ideas on how I can re-educate my errant system? Thanks...

 

[namsag]

Send it to double physics an tell it to listen to laws on convection.

 

[r.bob]

He knows the laws well enough namsag, just refuses to obey them.

I can only assume it's some sort of blockage, but if the water can get around the system one way, why not the other (correct and presumably easier) way?

 

[Agile]

Have you tried the boiler without the CH???

I suggest you turn the boiler stat to maximum and run it from cold and see what it will do.

Tony

 

[r.bob]

Thanks Tony, yes, when it initially seemed air-locked, I closed off CH valve, turned to Max and ran the HW until it eventually cleared. It does seem to be weaker when the CH is on, but you would expect that. Just can't work out why it then goes the wrong way. The fact that it goes the wrong way is confirmed by feeling the temp of pipe a metre from each boiler connection, and either side of the tank.

 

[r.bob]

Have just repeated the procedure suggested by Tony, and without the CH on, it goes the right way round.

Could it be that the pump (currently on max, number3 , and sited 1m above boiler on flow)) is too strong and taking all the water from the top of the boiler?

Poltergeists?

 

[Agile]

You see it works when you do the things I suggest.

Your pump should be on 2 or even 1. Putting it on 3 probably causes the problem and once established in the wrong direction then continues.

Amazing what you can work out if you think a little bit.

Tony

 

[r.bob]

I agree entirely, but sometimes the thought patterns of us DIYers needs a little input of extra knowledge/experience to make them more effective!

I had the pump on 3 because of the size of house, height of head and the large bore of the CH pipes (3/4" iron!)

I assume that thinking was wrong. Am I also right to assume that because the system is not fully pumped, then 1 or 2 would do? What would the symptoms be if I had it on too low a number for the system...I thought that might overwork the pump, like trying to do 30 in first gear! Or perhaps I mean trying to do 20 in top gear?

Lots of thinking Tony, but is any of it right?!

 

[JohnD]

while Tony's out at lunch...

the faster the pump runs the noisier it is, and might cause other problems.

If it circulates the water adequately round your house at a low speed, that's all that's needed.

If you find after a while you need to turn the speed up, then maybe sediment is building up and obstructing flow.

OOI, what colour was the water that came out, and did you see any sludge?

 

[r.bob]

Thanks JohnD. Yes the pump was a bit noisier than before. I did replace the pump while the system was drained. The old one was dated 1959, was almost silent and was on setting 3 out of 4. It's now in Derby museum. I've turned the new one down to 2, but will try it on 1 as well to check if flow is ok on that.

The water was very clean when draining, but I did notice a little sludge build up just inside the rads when replacing valves. The circulation does seem good though, and all rads are hot.