Cold radiators - one warm pipe and one cold pipe

[markmav]

Hi, I was wondering if someone might be able to give me some pointers. First off I'd better say that I'm not a plumber.

This is at the mother in laws house, so hopefully I can earn some brownie points. She has had plumbers out in the past, I think she'll have to get another, however...

The problem:

All the radiators in the house are cool/cold - the 2 pipes that connect to the radiators, one is boiling hot and the other is cold - this is on every radiator.

The cold pipe has a 'valve' on top with a plastic knob that I can turn, it has the word Cosmos on it with a + and - symbol. The Hot pipe has a plastic cover on it, if I take it off it has a 'valve' that looks like I can adjust with a screwdriver.

I've bled all the rads, water comes out of all of them. I've searched on here, and subsequently I've bled the pump (next to the hot water boiler) - water came out, and I've hit it with couple of times with a sharp bang (cut my knuckle in the process!!)

I'm not sure what type of central heating system it is - in the loft there is a cold water storage tank and next to that is a smaller tank, a feeder tank? Both tanks have water in them.

The boiler (in the kitchen) is a Baxi Solo 15HE - it has 3 lights, Lockout, Burner and Mains - the only light on is Mains - it's green. We've tried pressing the Reset button (for 20 seconds) - makes no difference.

Not sure if we have one problem (the rads) or 2 (the boiler).

Thanks
Mark.

 

[plumbersmate1]

Is the programmer on? Is the central heating on? Is the room thermostat turned right up?

 

[JohnD]

is there a hot water cylinder? is it surprisingly hot? what happens if you set HW to off and CH to on?

is the pump surprisingly hot (hotter than the pipes?)

is there a three-port valve? how many of its pipes are hot?

 

[markmav]

The Programmer is 'on', it's set to constant
The room thermostat is turned to the highest setting
And yep, the central heating is on.

 

[ukrobj]

Mark,

Try shutting down all rads except one and see if that gets hot. If it does, then open the next see the effect on the first etc.

There may be a block in the return to the boiler.... if opening the rad doesn't work, drop some x800 into the system, drain some out so the x800 gets into the pipework.

 

[markmav]

The pump is very hot

I can't actually touch the tank (insulation preventing me), but the pipe leading/going from the top is very hot

3 way 'port' valve - coming from the pump there is a pipe that then splits 2 ways (with a white box on top called 'Unishare', Port A = CH, Port B = HW) - all 3 pipes are very hot.

 

[JohnD]

it is not clear from your reply, but it is possible that the flow from the boiler is going to the cylinder. In this case it will not let much go to the rads. That's why I need to know what happens if you turn the HW setting on the programmer to "off" but the CH to "on". If you do, then flow should stop going to the cylinder and after a while, the pipe to and from the cylinder should start to cool down. Does it? The flow should then start going round the radiators.

Is the pump hotter than the pipes it is connected to?

is the water from the hot tap surprisingly hot?

 

[markmav]

it is not clear from your reply, but it is possible that the flow from the boiler is going to the cylinder. In this case it will not let much go to the rads. That's why I need to know what happens if you turn the HW setting on the programmer to "off" but the CH to "on". If you do, then flow should stop going to the cylinder and after a while, the pipe to and from the cylinder should start to cool down. Does it? The flow should then start going round the radiators.

Is the pump hotter than the pipes it is connected to?

is the water from the hot tap surprisingly hot?

Hi John,

I've just turned the Hot Water off, I'll leave it a few mins and see what happens.

I'd say the pipes connected to the pump and the pump itself are the same temp - very hot.

Yes the water from the hot taps is very hot.

 

[JohnD]

Yes the water from the hot taps is very hot.

Aha!

strapped to the side of the cylinder should be a cylinder stat. It will probably be set to about 60 ° If you turn the pointer using a screwdriver, it will click as it passes the Actual temperature.

What we want to do is to try to stop all the boiler flow going to the cylinder. Turn down the cyl stat to a lower temperature (50 ° will do, but you want it to click below whatever the current cyl temp) That should cause the flow from the boiler to shut off. If it doesn't, then you have a fault in the motorised valve, or possibly an electrical fault.

 

[markmav]

Hi John,

here's the current status:

The pipes to and from the radiators - where as before, one was very hot and the other cold (on all the rads), now both pipes (on all rads) are luke warm to the touch.

The rads are no longer cold, some are warmer than others - downstairs are warmer.

The pump (next to the hot water cylinder) - I've felt it a few times, some times all three pipes (one leading into and 2 leading from) are very hot, other times they are quite cool'ish (luke warm) - the pump remains very hot though.

I turned the theromstat on the hot water cylinder down to 50 - and the hot water setting on the controller is 'off'.

 

[JohnD]

if the pump is hotter than the pipes connected to it, then it is jammed, or dry, or obstructed, for example with sludge and sediment. The water flow normally prevents a pump from overheating. If you have an open-vented system, with a feed and expansion tank in the loft; and if the system, or parts of it, are quite old, then you can expect to have dirt and sediment in the system. Have you got an F&E, and does it have mud in the bottom?

If both the flow and return on all rads is now warm, then you are getting some flow through the radiators. You have got to establish if the flow to the cylinder is still going even when HW should be off. Leave the HW off and see if the cylinder continues to be heated.

If the pipe going to the cylinder is hot even when the HW is turned off, at the programmer or the cyl stat, then you have a fault. typically a worn-out motorised valve, but it might be an electrical fault. You really have got to feel the pipe going to the cylinder and verify if the flow ceases when HW is off, and restarts when you turn HW on.

 

[markmav]

Hi John,

I'm not sure if it's a F&E system - in the loft there is a large cold water storage tank (big round plastic thing).

Not far from that there is a much smaller tank with a ball cock/valve (like in a toilet) in it. It has a pipe leading into it (to the ball cock/valve), an overflow pipe (white plastic), a pipe leading from it (on the side towards the bottom) and a pipe bent over the top (I assume if there's too much water in the CH system, this flows into the tank?).

There is some sludge/dirt in the bottom, but below the pipe that I assume feeds the CH system.

I've been told that the CH is old.

I'm not sure I follow what you're saying here:
"If the pipe going to the cylinder is hot even when the HW is turned off, at the programmer or the cyl stat, then you have a fault"

I've attached a diagram of what'is upstairs with regards to the cylinder, pump etc.

It's pipes A,B,C and D that keep going hot and cold - the pump however stays hot.

with the HW water turned off, the boiler downstairs does now keep firing up, in fact is seems to be firing up and off very regulary - whereas earlier today all it had was a green power light.

CH

• markmav
• 24 Oct 2010
• 1

 

[JohnD]

I'm glad to hear it is firing up regularly and it seems to be circulating round the radiators.

If you can, leave the CH on and the HW off overnight, and in to the next day, until the hot taps run cold. (they may stay hot even though the HW is set to "off", which will be significant)

If, until now, a lot of the boiler flow was circulating through the cylinder, that would cause the radiators to be cold, and the boiler not to fire much. You need to keep feeling the pipes to and from the cylinder, and to and from the radiators, to find out where the boiler heat is going.

 

[markmav]

Hi John,

Thanks for your help so far - especially at this time of night on a Sunday.

"If, until now, a lot of the boiler flow was circulating through the cylinder, that would cause the radiators to be cold, and the boiler not to fire much."

That seems to sum up what has been happening this weekend. I'll tell her to leave the hot water off tonight and tomorrow, I'll drop in and feel the pipes tomorrow and tomorrow night.

many thanks
Mark.