Tearing my hair out!

[rolyatescort]

Hi Guys,

I have asked a few questions lately which a few of you have kindly helped with, thank you.

I have a Potterton Puma 80 Combi Boiler with a Myson Pump feeding 8 rads (4 up, 4 down). The heating has been off since last winter and after being put back in to use is barely working. I have always had difficulty getting the downstairs rad furthest from the boiler to stay warm. If i turn off all other rads it will heat up but as soon as i put another rad on anything more than luke warm the furthest one goes off. The house is absolutely freezing. However i try and balance i can not get more than a couple of rads to stay even warm.

All rads are bled and appear free of air. I have tried bleeding the pump through the big black hex bolt in the middle and can get a very small amount of water from there but little else. The aav is open and appears to be functioning. Expansion vessel isn't letting in water. System has been drained, EV pressurised to 1.5 bar, system refilled.

Any ideas? Could there be an airlock, if so how can i shift it? May it be sludge build up?

I have spent hours searching and am willing to search more if pointed in the right direction, but saying that please explain as much as possible.

Thanks in advance.

 

[JPC]

could it be the pump ?

 

[Softus]

How does the Puma behave? For example, for how long does it heat the CH water? Is your DHW water hot enough? What's the temperature of the hot water as it leaves the boiler?

Also, do you have dripping or leaking hot taps?

 

[rolyatescort]

DHW is readily available and very hot. The CH hot pipe coming from the boiler is hot and in time all the rad feeds are hot. The rad nearest the boiler can be hot within a matter of minutes but the whole system won't get hot even if left for hours.

The boiler fires up as you turn the heating on but doesn't seem to work very hard after that. There is also occasional but not consistent pressure increase at the boiler.

All hot taps in the house are fine.

 

[Softus]

So far, the symptoms are consistent with the following conditions:

1. Failed pump;
2. Failed electrical supply to pump;
3. Worn pump;
4. Sludge in the system.

Moreover, conditions 3 & 4 often go hand in hand - if the system has run without a corrosion inhibitor for, say, years, then the effect on the system is to clog up and the effect on the pump is to wear it prematurely.

If nobody has any better ideas, I would drain the system and observe the water that comes out, to gauge its general health. If it's very dirty and/or sludgy, then spend some time flushing it out (see the abundant topics that cover this), and then re-fill and 'see how it goes'.

If that doesn't do it, then consider replacing the pump.

Whatever you do, don't leave the system unprotected long term - you may wish to take advice from the boiler manufacturer as to which particular brand of inhibitor they recommend.

 

[rolyatescort]

Thanks for that Softus. I have drained the system very recently so do know the condition of the water. A couple of the lockshields were leaking a very rusty orange water which is also often what appears when bleeding the rads. Water drained from the system/rads is often very black,misty, in general very dirty.

I have lived here for over 3 years and am ashamed to say that the system has not be flushed or protected whilst in my ownership.

Are these things easy to do? (i have done all previous work myself and have no problems with draining down, removing/replacing rads, etc)

As for the pump, how easy is it to swap? Is there a test i can do to see if it has failed? What is a good reasonably priced model to exchange it for and where should i shop?

Sorry for all the Q's but i'm taking advantage of your replies while i can!

 

[nstreet]

I have always had difficulty getting the downstairs rad furthest from the boiler to stay warm. If i turn off all other rads it will heat up but as soon as i put another rad on anything more than luke warm the furthest one goes off.

Have you tried balancing the system first before you start replacing things.

 

[rolyatescort]

Yes as original post system has been balanced several times to no avail.

 

[nstreet]

However i try and balance i can not get more than a couple of rads to stay even warm.

Oops, missed that sentence.

 

[meldrew's_mate]

I'd go for Softus' solution with one caveat

Drain the system whilst hot, then, if you have a normal drain point at a low point in the system, trickle water out as you top up from the filling loop with the system running. With some luck this will clear most of the major deposits from the rads and pipework, enough to determine if sludge is the major cause of the malfunction. Use a rubber hammer to gently tap the lower edge of each rad to loosen harder bits.

Following this replace the pump, the standard one is the 6m head Myson pump, now called Circulating Pumps (CP6 ?), available at the Plumb CentRE.

Don't stop there if full operation results, there is still the important flushing procedure. Buy a good quality sludge remover (Sentinel, Fernox, etc) and follow the instructions. Then add corrosion inhibitor to complete.

It's worth noting that if you have no leaks you will never have to top-up the system pressure, and each time you top up you will dilute the inhibitor. Keep this in mind.


And finally my caveat. I once had to replace the main heat exchanger on a Puma because it was partially blocked with something that flushing chemicals nor powerflushing could shift. I hope this isn't your problem

 

[rolyatescort]

Thanks for that advice i'll be giving that a go.

My only problem is that the drain point is on the return to the boiler about 3ft of pipe from the boiler. The pipe the drain is on is actually about 8-10" higher than the height of the 4 downstairs rads. I assume this will have a negative effect on the procedure?

My alternative would be to remove the rad that is lowest down (which coincidentally is the one furthest away which i have most trouble heating) then get the system hot and drain via a hosepipe connected to the available lockshield. Flushing the removed rad seperately, is that a viable option?

 

[Softus]

... is that a viable option?

Sounds both viable and immensely sensible. Please post the outcome so it can be added to the knowledge pool!

 

[rolyatescort]

I shall do that this weekend and post the results. Keep your eyes peeled.

 

[kier]

do you have any dripping hot water taps,shower mixer dripping or could hot water be seeping into a washing machine or dish washer or any slight water leak on hot water outlet to above.(this will keep boiler in hot water mode and give poor flow to rads)
taps are easy to look at.are they dripping.
next check,turn off main water service valve on inlet to boiler,use a screwdriver in the slot,after 10 mins does the rads get hot,if rads get hot now its the above.ie cold mains water moving through boiler.
if above all correct its probaly your pump or the diverter valve is seized in hot water mode.
pump head is easy to change.

good luck
t

 

[Softus]

I shall do that this weekend and post the results. Keep your eyes peeled.

Ouch