Quick question I'm sure you'll know the answer to!

[Chivas69]

On my combi boiler, if my diverter valve was sticking or not moving as freely as it should be, could that cause some of my rads to heat and some of them to stay cold? Or is it one or the other?
Having probs with 2 cold rads and have tried everything and now after days of googling it seems it may be the diverter valve! However I thought if it was sticking on hot water I'd get no heat at all in rads?
btw the rads that get warm are very very hot!

Many thanks for looking!

 

[D_Hailsham]

1. Was the system previously working OK and this is a new problem?

2. Do you have thermostatic valves on the rads?

 

[Chivas69]

Yes and yes! All rads apart from 1 have trvs! All trvs working fine!

 

[D_Hailsham]

If the cold rads are furthest from the boiler, it could be the pump or the diverter valve. A weak pump would not be able to circulate to the more distant rads; and if the DV was stuck partly open the water would tend to take the easier route, via the HW exchanger, robbing the CH side of flow.

 

[Chivas69]

Thanks for the reply
I'm thinking Diverter valve myself! Pump seems fine and am getting hot water to taps! About 2 weeks ago my daughter said no hot water came out of a tap whilst I was out! When I got back it worked fine so I put it down to her turning the cold tap by mistake! Seems maybe the diverter valve was the problem!
So would the rads still heat upstairs if this valve was faulty? By convection maybe? Or would none work!

 

[D_Hailsham]

A correctly working diverter valve can be in either the CH position or the HW. This means that, when HW is running, the rads don't get heated up.

If the rads continue to get heated when HW is running, it means the DV is faulty; either sticking between CH and DW position, or the diaphragm is leaking.

Let the heating system cool right down, then draw off some hot water. If the flow pipe from the boiler to the rads gets hot, you know the diverter is the problem.

 

[Chivas69]

Thanks for the reply!
I'll try that once it's all cooled down!

It's a Ferroli boiler and it seems the diverter valve is a very common problem!

 

[Chivas69]

I ran hot tap when system was cold and the flow or return pipes for the rads did not get hot! Although the hot tap itself wasn't exactly very hot, I could put my hand under it just about!
If the diverter was only partially stuck would that explain the above?
Thanks

 

[D_Hailsham]

Diverter valve seem to be OK.

You said earlier that the TRVs are working fine. How do you know?

Shut off the rad valves which heat up OK. Do the other rads then get hot?

 

[easyflow]

Are the lock shields other side of the rads fully open ???

 

[Chivas69]

Trvs I took off and checked pins! Lock shields on cold rads are open ! I've closed off all rads but cold ones and still no heat! I've also checked pipes to cold rads and they're clear! Manifold also seems clear! Pump seems to be working!
Thanks

 

[D_Hailsham]

Trvs I took off and checked pins!

The pins may be going up and down but on some TRVs the pins are not directly connected to the part which controls the flow. So the valve is stuck shut even though the pin is up.

Tap the side of the valve with a hammer (take head off first). It might free up the valve.

 

[Chivas69]

I've actually undone pipes to trvs so know water passes through both sides! Also the one in the hall that's cold doesn't have a thermostat valve!