When CH is on, water drips into expansion tank.

[bobmoo79]

Hello I'm new to this forum and to central heating systems!

I have just moved into a 1930s house with open vented central heating system
A while ago I noticed that the central heating comes on when only hot water is selected on the control box and worked out that the fault must be with the motorised valve. I have a replacement valve (well the backplate and ball as the electronics are working fine) but haven't yet fitted it.

Yesterday I noticed another problem in the loft. When I am running the central heating water is dribbling into the expansion tank. This is a constant trickle (i.e. more than just frequent drops) when the heating is on, but when I switch the heating off it stops. I have reduced the CH pump to the lowest speed setting (it was on the middle setting) and the trickle is reduced to a frequent drip (about 1 per second).
The radiators are getting warm when this is happening.

As I'm new to heating systems I wondered what could be causing this problem? Can anybody here help?
If this has been happening for a long time is it possible that there is no inhibitor in the system?


Many thanks!

 

[gas_man_gaz]

sounds like theres a bit of muck in ya sys.. iam guessing its a 3port valve that is passing?
the pumping over is prob caused by the "H" being restricted/blocked, will need chopping out and cleaning/repiping..
wen the heating is on have ya noticed any of the rads have cold spots?

 

[bobmoo79]

Yeah, the downstairs radiators do have cold spots at the bottom (in the middle) so I though there might be some muck in there. If this is causing the overpumping is it imperative to get it sorted soon? I was going to leave that until the spring. Is powerflushing the only option, or is there another good solution? The system is pretty old and I don't want to cause myself more trouble at this point by uncovering any weaknesses.

Yes, the valve is a Honeywell 3port valve. I checked the electronics and it seems to be working fine, so I guessed I only needed to replace the backplate and ball. I'll need to drain the system (at least partially), but the downstairs radiators don't appear to have a drain point (I haven't checked under the floorboards). I was going to fit a self-cutting valve to allow me to drain the system to fit the replacement valve backplate. Are these a good idea? Can they be left in for long period of time without leaking?

Please forgive my ignorance, but what is the the "H"?

 

[doitall]

The MV won't cause the problem, a dirty system and or blocked cold feed will.

 

[gas_man_gaz]

what boiler have ya got?

the "H" is where the cold feed and open vent tee into the sys. it norm is above the pump in the airing cupboard and norm looks like a "H".
a good indication that it is blocked is by tracing a strong magnet over the pipework
i would sort it as soon as possible as it can cause alot of probs.

if ya good at diy ya could prob do a reasonable job by cold mains flushing, but it would take a good day n a fair bit of work.

dont use the self cutting drain, will cause more work and theres no need to.

 

[bobmoo79]

I'm not sure of the exact model at the moment because I'm not at home, but I know it's a Potterton.

What's the best option for draining down without a draining point?


I'll check out the "H" tonight when I get home.


Thanks

 

[kevplumb]

won't hurt to put some cleanser in the system and let it run round
before you change anything

 

[doitall]

There should be a draincock somewhere, possibly under the ground floor if wood.

 

[Agile]

Or if you are really lucky on the outside!

You might be able to clear it with chemicals but they might cause rads to leak.

It may need to be power flushed.

You could try X800 with the heating running for 3-4 hours and then drain from somewhere.

Its unlikely to deal with cold spots on rads though.

You MIGHT be able to deal with them by removing rad to garden and using a hose but that rarely works on double panels.

Tony

 

[gas_man_gaz]

if ya gonna do a cold mains flush at the same time ya could remove a rad and use the rad valve as a drain point.
depending on the type of rads ya got ya could remove the bleed plug and temp fit a drain in its place.
but if ya only going to replace the 3port and unblock the pipework i wouldn't fully drain the sys anyway, id bung the cold feed and use a few towel's and a rubble bag

 

[Agile]

DIA and I dont think the motor valve is the cause of the problem !

Tony

 

[bobmoo79]

Thanks for the info guys.

If I drain a rad and remove it then use the rad valve as a drain point, is there an adapter (i.e. hose barb) I can use to attach a hose to the drain valve?

 

[doitall]

Depends on the type of valve.

A few pics of the important parts may be an idea.

 

[gas_man_gaz]

depends on the type of rad valve some ya can use a 15mm compression nut and olive n a bit of 15mm pipe