Central Heating Refresh

I have an open vented Y-Plan CH system, now 15 years old. The house is a mid-terrace two bed 2 floor house

It's been running OK apart from issues with the Myson 3 port valve, sometimes the actuator doesn't turn unless persuaded with a punch! I have noticed the spindle on the valve body was rather stiff and wasn't sure if a new valve would be so stiff. After 15 years I am on the fourth actuator and when I discovered the valve is stiffer than a new Myson 3 port valve, I decided it was time to replace it.

The Myson pump does run quiet and there are no issues but I thought "What the heck"... so I'll be replacing this with a Grundfos Alpha 2L, more electrically efficient and quieter, how quiet in comparison to the working Myson will be interesting to hear.

The Potterton Suprima 30 boiler is serviced once a year by a local gas engineer, the PCB was replaced years ago (a well known fault).

The schedule is to undertake this overhaul on 2nd May. In preparation and 3 weeks ago I drained the system, cleaned out the FE tank which had a bit of rusty sediment (that I scooped out and mopped up with an old cotton t-shirt - I won't be wearing that again). Then with the Sentinel X400 system cleaner to hand and beginning a refill I noted the ballcock was rather manky looking and bunged up with calcium deposits and struggled to work at all, so I sped to Screwfix for a replacement and duly fitted.

In addition to the pump I have also two new pump gate valves just in case.

For the inhibitor I'm going to use Fernox MB1.

Today I decided to get a filter and have gone for the Spirotrap MB3. This will go on the return pipe above the boiler which is in the kitchen. It will be visible, which is one reason why I went for the Spirotrap as it's the best looking filter. Also, from the things I have read on filters, it appears to be the most reliable in terms of not leaking.

The Alpha pump is a nice bit of kit, however there is an issue in your setup. While the pump makes for a nice system where the flow rate backs off as the TRVs shut down, you have a boiler which has a minimum flow rate - I think you can see the conflict there. I'm sure many boilers will go well below the flow rate the instructions say, but the control gets more and more difficult - and many will start boiling which is bad for the boiler and noisy.

Also, if you are changing the valve, then I'd probably be tempted to replace the 3 port valve with 2x2 port valves (ie S plan) which I suspect are more reliable overall. Also, if your layout supports it, you can add a third valve and split the upstairs and downstairs heating.

I don't doubt the potential issue with flow rate with said pump but the house is open-plan downstairs with no TRVs to shut off (the room thermostat is in this area). Plus the bathroom rad has no TRV (it's the first rad and always on) so I'm confident the flow rate will not be an issue.

Scarum said:

It's been running OK apart from issues with the Myson 3 port valve, sometimes the actuator doesn't turn unless persuaded with a punch! I have noticed the spindle on the valve body was rather stiff and wasn't sure if a new valve would be so stiff. After 15 years I am on the fourth actuator and when I discovered the valve is stiffer than a new Myson 3 port valve, I decided it was time to replace it.

Click to expand...

Do you make sure that you fire up the system a few times over the summer?

ban-all-sheds said:

Scarum said:

It's been running OK apart from issues with the Myson 3 port valve, sometimes the actuator doesn't turn unless persuaded with a punch! I have noticed the spindle on the valve body was rather stiff and wasn't sure if a new valve would be so stiff. After 15 years I am on the fourth actuator and when I discovered the valve is stiffer than a new Myson 3 port valve, I decided it was time to replace it.

Click to expand...

Do you make sure that you fire up the system a few times over the summer?

Click to expand...

I hear what you're saying, good call. I'll do this in the future with the new valve.

I achieved 80% this weekend, all except the pump which as I feared, I could not move the pump union nuts. Stuck fast. I've never hacked and cracked through one of these before and as space is at a premium to wield a hacksaw, I'm considering whether a Dremel might do the job (I don't own one, yet).

After one month of sludge cleaner in the system, all that came out was rusty coloured water and hardly any particles.

In the end I didn't (couldn't) remove the 3-port valve body (stiff nuts) but I replaced the sticking spindle.



You can see the rust encrusted spindle and PTFE "shoes" which look quite worn and as I thought, the new spindle moves freely inside the valve body. Consequently the boiler hasn't had any flashing LED standby issues (because the actuator couldn't move the crusty old spindle).


The Spirotrap filter is fitted. It was impossible to squeeze it in to the pipe cut-out above the boiler because of no flexibility / movability with the pipes, so I had to get a straight coupler and some copper pipe to fill in. I just need to sort the plaster that's come away from the ceiling around the pipe, or fit pipe insulator (?)


System refilled with Fernox MB1. I've got red hot rads and very hot water!

So, as for the pump, I could either:

1/ try to crack the nuts (buy a Dremel?),
2/ cut the copper pipe either side of the pump valves, fit straight couplers and fit the new pump and valves on to new copper pipe
3/ get myself some Popeye arms
4/ of course I could get a pro in...

Have you room to get at the pump union nuts with a hammer/chisel ?

If so, then put the chisel on a flat of the nut, off centre so the blows will tend to undo it, and with the width of the point across the thickness of the nut. The blows will tend to undo the nut, and if it doesn't move, will tend to split it.

Alternatively, can you get to undo the pump from the impeller housing ? If so, then fitting the new pump onto the old body would be an option if it's not too bady corroded (either corroded away, or built up with "crud".

I did try cracking open one nut, it didn't budge, bigger hammer required? Afterwards, with the system refilled, I noticed a minute amount of rusty crud weep through (when the pump was on) which solidified in to a rusty nugget. Nothing to worry about I guess.

Bizarrely, I discovered yesterday after 2 weeks since completing the above that the pump has now actually failed! I'm glad I planned to do all this in warmer times, be that a lesson to us all

I'm going to soak the nuts in WD-40 overnight and try again.

very big spanners will do it. I guess you are using pump pliers or something.

I am lucky enough to own 18" and 24" stilsons which have plenty of leverage. Some people use small ones with steel pipe over the handle. It is essential to use two at a time so you don't put any twisting torque on the pipes.

Correct, pump pliers.

In fact I'm going to hacksaw through the nuts then get a screwdriver and twist-crack them open.

Another possible technique, but obligatory warning THIS CAN BE HAZARDOUS

IF you have a small gas torch AND you can get to the nuts safely then heating the nuts up will often crack the rust/corrosion that's probably holding them tight. It's a common technique for dismantling stuff (eg on vehicles) where a quick application of an oxy-acetalyne torch will often free up nuts that appear totally stuck. The trick is that you need to get a lot of heat into the nut before it can conduct into the bolt (or in this case, union) it's screwed onto - that way, the nut expands and in doing so pulls apart the layer of corrosion that's "glued" it in place.

As I say, this is somewhat hazardous, and only to be undertaken if you are sure you can do it without setting fire to or melting anything. In particular, it's easy to overlook electrics and melt a cable

Also, you need a decently hot gas torch. As I say, the trick is heating up the nut faster than what it's screwed onto so you get differential expansion.

SimonH2 said:

As I say, the trick is heating up the nut faster than what it's screwed onto so you get differential expansion.

Click to expand...

I've done that on cars using the single-contact brazer on an Oxford welder.