Central Heating Flow pipes burning hot - Return Pipes cold

[Jodi Thomson]

Hello Folks.

Looking for some extra advice regarding our new CH System. We recently replaced our Old Electric System with a Worcester Greenstar Camray Condensing External Boiler (Oil) which has been connected to a new Megaflow Systemfit within the house. We had some problems after installation which we posted on this site, and a very helpful guy gave us the no. for a Aberdeen based plumber. We did contact him, but he never got back to us, so finally got hold of another one, who has spent the last 2 days checking over every part of our system: -

All Megaflo System working as required (plenty of hot water) including motorised valves, pump, pressure vessel etc (and plenty of hot water).
All pipework in correct places (double checked this by swapping pipes just in case)
Whole System was Power Flushed this morning for 5 Hours.

Problems still arising: -

No return flow on rads. Flow pipe coming in so boiling hot, no circulation.

Have tried heating rads one by one. This works and all rads get roasting, but turn on more and the heat dissappers, return pipes still cold. Have tried balancing to no avail. The plumber has said there must be a blockage somewhere in the pipework, but where, we have no idea. We had tried power flushing but it has not shifted the blockage. Is there anything else we can try, as we really don't want to have to go change all the pipework. Is there a different stronger chemical we can try? Any ideas would be helpful and much appreciated.

 

[tamz]

Powerflushed or not it worked before so there is no reason why it would not work now especially as it has been repiped.
Have they checked the pump valves are fully open?
Unfortunately it can sometimes be quite hard to diagnose something where you can't actually see/feel what is happening.
Here is an easy way to check if the problem lies with the megaflow set up or the system.
Get a couple of bits of speedfit and join directly to the flow and return from the boiler to the rad circuit and put the pump onto the bit speedfit. This will cut out anything to do with the cylinder and can be done quickly. If it works then the problem is with the way the megaflow has been connected or set up.
12m away from the boiler for the pump is not a problem even for a 15-50. What size pump was on the electric system and what size house is it?

Btw fyi. Having the certs doesn't mean you actually know what you are doing, just that you know the regs. Nowadays they seem to get given for good attendance as nobody fails anything anymore. Personally i don't see the problem in telling someone they are useless at the job if they are

I had to water the last bit down there as Redsaw or Puddle would have been on my case

 

[Jodi Thomson]

I will get my partner to try this with the speedfit fittings on Sunday, and test it. The pumps we had on the oldshurchill system which did the CH & DHW (a huge kettle) were grundfos 15/50 x 2, with a major brass fitting inbetween them. We now have a Grundfos 15/60 (only 1) which came fitted on the megaflo, and have replaced it already to rule it out. Our house is 4 bedroom - 1 bathroom - 2 shower en-suite. Our KW for the rads was under 18,000, and our boiler is a worcester 18/25. I am loosing trust in plumbers in general within NE Scotland, i think we must get all the ones that fried braincells at school!! Its not easy getting a great competent plumber without them costing an arm and a leg.

 

[tamz]

I am loosing trust in plumbers in general within NE Scotland, i think we must get all the ones that fried braincells at school!! Its not easy getting a great competent plumber without them costing an arm and a leg.

You'll be near Peterheed then . Been there a few times.

I know loads of guys, me included who do work up that way but the money has to be good to consider it.
Usually you get what you pay for and if they pay the premium then i do it. I've got my eye on a quality zimmer and it aint cheap

 

[Jodi Thomson]

Aboot 20 mins from Peterheed - nnae too far. I always like to use self employed guys with smaller companies rather than the larger companies we have in this general direction. Were self employed ourselves , so like to use the local boys, keeping the work going in the area, doing our bit for the community and all that!! If the options i've been given from yous tonight don't work, then i may just purchase that zimmer for you. White gold? !! He He

 

[tamz]

The pumps we had on the oldshurchill system which did the CH & DHW (a huge kettle) were grundfos 15/50 x 2, with a major brass fitting inbetween them. We now have a Grundfos 15/60 (only 1) which came fitted on the megaflo, and have replaced it already to rule it out.

You may just need a bigger or additional pump fitted if your house is well spread out

 

[Jodi Thomson]

Can we fit an additional pump - another 15/60, as we have a spare handy. Our plumber said we could not fit another one on the system beside the original one as they would not pump in sequence or something along that line, is this incorrect?

We have a normal sized bungalow - livingroom at front with large rad, diningroom/kitchen backing onto livingroom, rads here are back to back, and the bedrooms come of the side of these. House length must be around 24 metres, and two rads upstairs (one is a towel rad and works as a bypass as no TRV fitted)

 

[tamz]

24m long house is quite a spread for a 15-60. It can be worked out to see what pump head is needed.
If you have another pump use it as big pumps cost big bucks.
You can put another pump on without causing any problems. Just wire it through the heating motorised valve so it only comes on with the heating. Stick it on the main run return.

 

[tamz]

24m long house is quite a spread for a 15-60.

Especially pushing through 22mm (i just remembered you had mentioned that wan)

 

[Toddyplumb]

Half way down the bungalow connect flow and return together see what happens

 

[TheGasEngineer]

... As I said last time and as Tamz has just said it should not be that hard to solve , you just need ... a bit of logical thinking ...

Toddyplumb is right on all counts and you have it within you to think it through. I suspect you're in headless chicken mode and you need to get out of it. Sit down and think logically and make a plan. Draw the circuit and plan to pump-test each bit. I'm serious here. You have to ask the obvious questions and the answer will be staring you in the face. It's true though - if you want to hide something, put it in plain view. Humans have a habit of ignoring the obvious...

After all, you are only trying to find a blockage. And actually, it would be possible to use lengths of plastic barrier pipe running around the house to bypass different sections. This could be a useful fault-finding tool and a temporary solution while the offending pipe is replaced.

Look at my previous post about removing a rad and disconnecting the boiler. Draw out the circuit. Plan which pipe runs to test and where to block the other pipe runs to achieve that eg by closing valves or using push-fit stop-ends etc (Use SpeedFit pushfits; they demount cleanly). Plumb the power flush into a rad tail (one pipe only - the return to the powerflush need not be used - use it to pump only and not collect return water).

Keep a record of each section that appears ok. That also has a value for obvious reasons.

Ureka moment!* a guess?? when a new boiler isfitted there are often plastic bungs in the flow and return. I wonder if they were removed. One may have gone down the pipework too. It's very unlikely but not to be discounted.

Don't move the pump for the time being. I could go into positive and negative heads but you only get that problem when the water is flowing... Eeek!

 

[doitmyself]

Hi Gas Engineer: - Whole Story so far: ...They did not flush the system when new boiler went in. ... Switched on - Circ Problem happened straight away.

At least you haven't paid the chap.

Another plumber in ... balanced rads

How was he able to do this if the return is cold?

You say that, if one rad is turned on at a time, it heats up OK but the return pipe is still cold. Have you checked that the lockshield valves are not closed?

You say that all 22mm cooper pipe has been replaced with plastic and the problem is still there. This would suggest that the problem is elsewhere.

If you disconnect both ends of the plastic pipe where it joins the rest of the system, close down all rad valves, connect a hose to one end of the plastic pipe and send some water down the hose, you will be able to check if the plastic pipe is clear. If it is, you will know the blockage is not in the plastic pipe and must be in the rest of the system, i.e before or after the plastic pipe.

 

[lewisplumber]

Are the rads on drops from the loft or are they under the floor? And just wondering if the rads have been bled? Stupid questions but these things are over looked.

 

[RTPS]

Have you got the flow and return the wrong way round on the boiler? just a thought
Also negative and positive pressures do not apply to a sealed system!

 

[tamz]

Generally in Scotland the houses all have solumns so most likely all under the floor.

 

[doitmyself]

Generally in Scotland the houses all have solumns so most likely all under the floor.

What's a "solumn"? Is it a Scottish word for cellar?