Poorly Netaheat 50e + wife doesn't "do" cold

[wobbin]

Hi,

Briefly, I have a problem with my Potterton Netaheat 50e which keeps tripping out - the overheat switch at the bottom of the boiler pops out and needs to be reset once things have cooled down. The output pipe around a foot from the boiler is very hot, and the return just warm, so looks like a flow issue. I can get hot water but all the rads are cold. Boiler stat is set between 2 and 3.

Have checked the following:

1. The C/H cold supply header tank is full.
2. The pump (Grundfos 15/50 about 4 years old - last replaced by me) is running.
3. Checked there was no air in the pump using centre screw bleed.
4. Still didn't trust the pump so have removed it, blown any silt out of the rotor using a pressure washer (very effective !) and have temporarily jammed the rotor and tried to turn the shaft - it wouldn't turn so I'm confident that the rotor has a good mechanical connection to the motor spindle.
5. Whilst the pump was out it became clear that there was a lot of black cack in the water so I suspect that when we had an extension built 2 years ago the "engineer" who re-oriented the boiler flue and added 3 rads failed to put any Fernox in the system afterwards. May his important parts turn green and drop off
6. In view of the above I have drained and refilled the system. Next step is to use something like X400 for a week or so followed by another drain down but I'm unsure as to how effective this will be if the circulation is poor to begin with.
7. Have temporarily removed the electromechanical gubbins from the (Honeywell V4073) Y plan valve and am satisfied that the shaft turns freely. The motor is fine and operates the valve when the DHW stat is operated.
8. Have bled, bled again, re-bled everything. Still no C/H

I think there's either an airlock or a blockage. I've tried upping / dropping the pump speed to shift residual air but there's no apparent sign of anything major at the bleed high points above the pump and the DHW outlet of the Y valve.

Any suggestions please as to what else I can try to restore domestic bliss ? My better half is saying that we should change the boiler (for a nice expensive Worcester Bosch...) Nice idea from a gas savings point of view but it seems clear that there's other issues which need to be sorted anyway.

Kind Regards,
Robin

 

[ChrisR]

Netaheat Profile, presumably?
Gravity or pumped HW?
What m valves/pipe configuration have you got from the boiler?
CH valve opening?

 

[wobbin]

Morning Chris, and thanks for your reply

Sorry, yes it's a Profile 50e and it's fully pumped.

Boiler (sited downstairs) output goes through an Airjec into the pump which then feeds centre inlet on the Honeywell Y valve (pump / y valve / airjec are in the loft)

As to whether the valve is opening to C/H I'm not 100% sure - the C/H feed pipe doesn't seem to get as hot as the DHW coil feed pipe does, though as I said in my original post the valve is not jammed and does move via the motor towards DHW port when the tank stat is set to demand DHW.

[Edit] Now that everyone in the house is awake I've been around again and re-bled everything. Nothing at all in the radiators and very little from the bleed points above the pump and Y valve.

I have the boiler on at the moment, with stat at 2, and the DHW cylinder stat at 55 degress. Boiler is cycling and hasn't tripped as yet after 15 minutes, but there's no sign of life from the radiators.

One thing I noticed last night when I had the motor etc off the Y valve was that with the lever in the manual position (which I understand should allow boiler output to go both ways) the position of the mechanism would have meant that the valve would not be in the dead centre position. Bearing in mind that the angle of rotation of the valve spindle is only very small I was thinking that this might have quite a dramatic effect on the valve operation ? Maybe something has become misaligned on the mechanism ?

As I write this the system is in DHW mode and the inlet and outlet pipes on the boiler are what I'd expect, output is very hot, return is hot but just bearable to touch.

I've just set the DHW to off on the programmer. The boiler stopped momentarily then restarted in C/H mode. Touching the boiler pipes now, the outlet is very hot and the return cooled within seconds and is now cold so that would suggest that there is flow across the boiler and that the valve is opening to C/H ?

Cheers
Robin

 

[ChrisR]

the valve is not jammed and does move via the motor towards DHW port when the tank stat is set to demand DHW.

A 4073 is a spring return valve. It doesn't have to move to be open to HW, unless the last position was CH only.

[Edit] Now that everyone in the house is awake I've been around again and re-bled everything. Nothing at all in the radiators and very little from the bleed points above the pump and Y valve.

Assume you mean no air - low water prevents circulation.. Checked the header tank?

If you had a severe sludge problem I'd still expect some rads to get hot.
The MAN position is just for venting really, not critical.

 

[wobbin]

Hi Chris,

Yep, header tank is hunky dory.

Boiler hasn't tripped yet (stat now at 3) but still have very hot boiler out pipe, stone cold return and stone cold radiators (and missus !)

Puzzled

Cheers
Robin

 

[ChrisR]

So where's the heat going then??!
Seems to be defying physics...

Are you on CH only?
Can you feel HW return pipe?
Looking like the pump. Are its valves open?
Was the rotor sludged up?

COuld be air in ch system? If you drain some water from a low drain point does the header refill?

 

[JohnD]

Does the pump casing feel very hot?

What about the pipes vound the pump and the valve?

 

[wobbin]

I'm beginning to wonder if my neighbour has a feed from my boiler

You got me going re the pump gate valves.... that would have had me blushing. Just checked and they're both open.

Boiler has now tripped once. I'm on CH only and we have the immersion heater switched on as the kids want a shower...

The DHW inlet pipe is hot, as hot as the CH flow pipe is, and the DHW return is cool.

There was some sludge on the rotor but this blasted off nicely with my pressure washer and it looked to be pristine when I refitted it. There was also a nice tight mechanical coupling between the motor spindle and the rotor, at least when it was cold though maybe as it heats up this isn't the case.

Forgot to mention that the programmer (Siemens RWB9) is a recent addition as the old unit developed a tendency to think it was midnight every couple of hours. System has been fine for 3 months on the new programmer previously.

Cheers
Robin

 

[wobbin]

Morning John, welcome to the party.... grab a beer

The pump body is too hot to hold, as are the pipes as well as those around the Y valve.

Cheers
Robin

 

[JohnD]

wife doesn't "do" cold

 

[wobbin]

I'll take one of those please, it's cold in my loft...

Cheers
Robin

 

[wobbin]

<Drum roll> Tada ! Sorted

Good news & some bad news too...

The problem was caused by an almighty airlock.

There's a drain tap on the return feed pipe just above the boiler. It was originally seized solid but eventually decided it would move which left me having to do some acrobatics with a length of hosepipe. Once I'd managed to free it and vent the pipe into a bucket there was a load of air present. This was also undoubtedly a useful exercise as it removed a load of sludge.

The inside of the C/H header tank has been cleaned before refilling and the system has a dose of X400 running around now which I'll leave for a week or so before draining again and refilling with a dose of X100.

The bad news ? Well as things were getting desperate (not least the Mrs !) I decided to go off any buy a replacement pump and a Y valve, which of course made no difference whatsoever

Ho hum... well the Mrs is toasty and I've earned some brownie points. As the Y valve was dated 1988 and the pump was dated 1999 (could have sworn I'd fitted that pump just a couple of years ago, how time flies !) I'm philosophical.

Thanks to all of you that replied to my pleas for help, and a happy new year to you and all on the forum

Kind Regards,
Robin

 

[JohnD]

... well the Mrs is toasty

I suppose you won't be needing these, then