Two Pump or not Two Pump? That is the question

[ukspid]

I watched my CH slowly degrade over the past months until I finally blocked it up completely with all my draining and flushing. Thanks to tips on this site I finally got some normality back - but it's not perfect.

It's a vented system. Did have a Myson Unit 3 pump which I replaced with a seemingly unused Grundfos 15/50 that has been in a box since we moved in 15years ago. It didn't solve the problems (but a weekend of flushing and additional venting did make a huge improvment).

I'm not convinced it's back to normal though and maybe the pump is not good enough (due age, storage and the fact I accidently ran it dry for 15-30 minutes) so will replace it with a Wilo Smart Pump. Note the pumping is into the system (i.e downwards) with an Aerjec just above.

My question is. If I still feel that there is not enough "oomph" in the system will fitting two pumps improve the flow? I was thinking of putting the spare one in the feed between the boiler output and the aerjec input.

I have flushed out enough gunge to halve OPEC oil prices so reckon the system is clean.

 

[Agile]

Never fit two pumps !

Either there is still dirt in your system or a pipework problem.

We always read these bold statement that " I have flushed my system"!

That is even questionable when it comes from a so called professional. Coming from a DIYer it really has no meaning!

I could ask what chemicals and power flushing pump did you use and where did you study the techniques for power flushing?

Tony

 

[ukspid]

Quick response. Thanks.

** I get the message - never fit 2 pumps! **

Don't think I said "power" flush. I've had some radiators (ones that just would not get warm) off and cleaned through with a garden hose.
Then I used mains water around the circuit, one radiator at a time, (connecting at the furthest and lowest radiator ports) repeated 2-3 times over a 2½ hour period.

System has greatly improved ... lovely hot water in (over 15 years old) cylinder after 20 mins and any individual radiator (some new-ish, some old) will now get too hot to touch.

Just about to start introducing more than one rad. at a time and that's where I'm expecting the same old trouble of not enough flow to keep them all going. Might be residual gunge or duff pump (or aerjec maybe?)

BTW: I'm offering shares in sludge if anyones got a use for it!

 

[ChrisR]

Even Fernox claim you can remove "up to 80%" !

Systems up to about 16-20kW are ok on a 15-50, IF it's working properly.
You determine whether it's doing its job by checking boiler temps and duty cycle.

 

[Agile]

It sounds as if your problem may be balancing then.

Close all lockshield valves and then open each just ONE turn as a starting point.

Then tell us what the result is.

When its stabilised the return should be noticeably cooler than the flow. Ideally about 11°C if you can measure it.

The Grunfoss pump should be fine on setting 2. There is no point in changing it for a Wilo ( sorry Dave ).

Tony

 

[ukspid]

Ok Hi Agile (if you're still watching!)..
In terms of estimated order of path length from the boiler (1 is nearest):


-----------------------------
Upstairs
1) Nice and hot
2) Cold
3) Fairly hot
4) fairly hot
-----------------------------
Downstairs
5) Just about warm
6) Cold
7) Cold
8) Cold

All TRVs at max
Boiler thermostat at max

Boiler cycle approx 4 mins on 12 mins off

Mild evening (5-6PM today)

Thanks in anticipation


.... and can I get a rad thermometer anywhere ..... not in Chelmsford on a Monday!