SMC twin pump (I think) Central Heating Prob

[Niggy]

After doing loads of research I think I have a SMC twin pump central heating system (after searching high and low for a diverter valve) but I can't work out why my radiators don't work properly.

If the heating is turned on, on the control panel, the boiler (Potterton Netaheat) fires up when lounge thermostat is turned up, as it should, but the radiators don't get hot.

The only way i can get the heating to work is by turning the thermostat on the hot water tank up high and this seems to make water pump around the whole system regardless of whether the switch is turned to h/w on or both h/w & c/h.

Why should this happen?? I'm pretty sure i can hear both pumps running in garage so I don't think its the heating pump (I may be wrong though)

By the way I have recently moved into this house (my first!!!) so don't have any experience with this system or heating in general.

Any help would be greatly appreciated (My better half is starting to complain of the cold!!!)

Thanks in advance

 

[Niggy]

Sorry for my impatience in bumping this but does anyone have any ideas or solutions to my problems or are there any checks I can make to find out what might be wrong????

Actually it might be helpful to confirm that what I have really is a "twin pump" system - it appears that I have 2 pumps in the garage but seeing as I have never seen a diverter valve before I cant be sure that I don't actually have one.

I also have a liitle box beside the pump in the garage with an arrow on which I am assuming is a non-return valve - I believe that this is a another sign that I have a twin pump system?????

I have been very impressed with how helpful people are on this forum and if somebody could give me some pointers then it would help me out a great deal.


TIA

 

[ChrisR]

Little box? err hard to tell what you're seeing from that.

If the ch is on and the hw off then just the ch pump should run. Use a listening stick, or disconnect its power while you think it should be on. It should be pretty obvious if its starting and stopping.

Here's a typical zone valve, a 3 port is similar with an extra pipe:
http://content.honeywell.com/uk/homes/Catalogue/Heating Controls/2.19 V4043.pdf

 

[Niggy]

Thanks for reply ChrisR

I'm pretty sure that I don't have any electrically operated valves like that and I have followed all the wiring i can see from boiler/control panel.

I'm also pretty sure that the c/h pump is operating when c/h is on but I shall check again when I get home.

Any ideas why the heating comes on when hot water is "forced" on by turning thermostat up on hot water tank???? If it is a problem with c/h pump - should this happen?

The "box" (bad description - i know) i was refering to is metal and approx 4"(L)x2.5"(D)x3"(H) as I recall. It has 4 screws holding a top plate to the main body and is about a foot away from c/h pump with an arrow on side pointing away from pump. It has SMC written on top plate.

I can't find anything like it having a look around some of the plumbing sites so can't show you anything like it i'm afraid

thanks again

 

[toasty]

That box sounds like a relay used to switch one of the pumps.

Search on the web for Grundfos, they do a twin pump system too.

Can you not take out the air bleed screw from the pumps and see which ones are running?

 

[Niggy]

There are no wires coming from the "box" at all - so don't think its controlling anything

I've found the site which made me think that the box was a non-return valve - see SMC controller layout although the pumps look a fair bit newer than the ones in the pic

http://www.gasman.fsbusiness.co.uk/fully_pumped_systems.htm

 

[ChrisR]

Good thought toasty but I don't think any of those SMC pumps had screws you could take out. As in "Sealed Motor " Co!

Looking at the piccy on the page you point to the one pump appears to supply the HW cylinder but is also connected to the route on to the CH. Yours seems to be sending boiler water both ways. I confess I dunno how it works. If the old b****rs on this site don't help try the Plumbing Pages forum - there's some good old b****rs on there who will remember!

 

[kevplumb]

the box is a non return valve
should be one on both pumps

 

[namsag]

grunfoss do a 3 port twin headed pump called a pump plan that will replace your smc arrangement without to much alteration

 

[kevplumb]

it will alter the bank balance tho

 

[brumylad]

The only way I can explain the behavior of your system is if someone had turned the non-return valve round to face the other way. I can't see how a modern non-return valve could fail so that reversed function occurred. However I remember seeing a drawing of an old non return valve somewhere and this used a metal flap. So I can see how wear combined with debris might produce this behavior. Bit of a long shot but it might be worth checking the valve.

 

[kevplumb]

aha the light goes on
with age comes
grey hair
wrinkles
EXPERIENCE

 

[ollski]

Well if the heating pump is running then the anti gravity valve will be faulty....if the valve is stuck then the water will just go round the heating circuit instead.

 

[kevplumb]

if my memory serves (altzhimers and all that ) there should be screws on the valve to open it up
probably seized solid tho

 

[Niggy]

Thanks for all your help

Havent had much time over last couple of days to look in garage but I'll try and double check that c/h pump is working and check out valve tonight.

Yes, kevplumb there are screws holding down top-plate on valve. I think I can isolate between c/h pump and valve but not other side so to remove the top plate in order to check valve I assume that I'll need to drain system?????