Microbore heating - Rads hot when only water selected

[Alan F]

Hi I Have a microbore system that has worked well until I cleaned the system with Sentinel due to sludge causing the pump to stop. Since then the two of the rads now get warm when only hot water is selected. Not sure why but any help appreciated. Thanks

 

[ianmcd]

Microbore system is just the size of the pipes, which boiler , what controls , posting pics of your set up is usefull

 

[Agile]

It is just possible that you have been very successful with your cleaning and exposed a design problem with the heating and hot water return positions.

But with system cold, start hot water and feel the ( so far unidentified ) outlet of the motor valve supplying the rads.

That should identify if the valve is leaking.

Sentinel is a manufacturer. They make several cleansing chemicals! You did not tell us which one you have used.

 

[Alan F]

Hi, it was installed in 1976, the boiler is a floor standing Indeal Standard E Type RS balanced Flue, the system only has one pump for the CH heating, no other controls except for a timer where you can only set for hot water only or for hot water and CH, you cannot set it just for CH only. In the loft is a header tank for the cystem which is not sealed.

We had a great CH engineer who improved the system by removing some of the dual entry valves and having two valves on some rads.

I used Sentinel X400. The system has worked well previously. If you need any more information please let me know.

Thanks Alan

 

[ianmcd]

Are the two rads that are heating when only HW is selected, upstairs radiators by any chance and were they the ones that previously had twin entry valves fitted ?

 

[Alan F]

No, these one are the original dual entry valves.

 

[D_Hailsham]

the system only has one pump for the CH heating, no other controls except for a timer where you can only set for hot water only or for hot water and CH, you cannot set it just for CH only.

You have a pumped heating, gravity hot water system. The boiler is turned on whenever there is a call for hot water and the HW cylinder is heated by natural circulation from the boiler (hot water rises, cold water falls). When CH is required, the pump is turned on by the CH timer and room thermostat. That is why you cannot have CH only.

Three possible reasons for your fault:

1. Faulty pump - normally a stationary pump provides enough resistance to prevent natural circulation through the rads.
2. Reverse circulation - water is going round the rad circuit in the opposite direction when only HW is called. This is caused by having the return from the CH circuit nearer to the boiler than the return from the HW cylinder.
3. Faulty anti-gravity valve - this is fitted on the flow connection after the pump.

You can check 1 and 2 as follows:

1. Select HW only; let the boiler heat up; compare the warmth of the in and out pipes of the pump (do this at least 1ft from the pump. The out pipe should be much colder than the in pipe. If there is little difference, water is getting past the pump impeller.
2. Run CH and let system heat up; check which of the two pipes connected to the problem rads is the hotter; turn of CH and let system cool down; turn on HW only and let system heat up; check the two pipes again. If the same pipe is the hotter there is no reverse circulation; but if the hotter pipe is now the one which was cooler when CH was running you have reverse circulation.

 

[Steelmasons]

You have a pumped heating, gravity hot water system. The boiler is turned on whenever there is a call for hot water and the HW cylinder is heated by natural circulation from the boiler (hot water rises, cold water falls). When CH is required, the pump is turned on.

1. Reverse circulation - water is going round the rad circuit in the opposite direction when only HW is called. This is caused by having the return from the CH circuit nearer to the boiler than the return from the HW cylinder.

On a gravity HW/pumped heating set up?..
You obviously fail to understand how a gravity HW pumped heating system operates.
Now if we were referring to a fully pumped system then it makes no difference whatsoever whether the cylinder return is the first or last Tee back to boiler as long as all heating returns are connected BEFORE the final connection to common return..
You are not a heating engineer nor do you install heating systems , until such time as you posses the knowledge then I suggest you refrain from giving any further advice.
I do hope you won't be arguing the toss.

 

[Phill Peck]

I do hope you won't be arguing the toss.

I guess not

 

[D_Hailsham]

Now if we were referring to a fully pumped system then it makes no difference whatsoever whether the cylinder return is the first or last Tee back to boiler as long as all heating returns are connected BEFORE the final connection to common return.

I asked you to justify this assertion in a previous topic and you have not replied. I assume, therefore, that you are unable to do so. In that case there is nothing to argue the toss about. The T rule applies.

 

[Steelmasons]

I asked you to justify this assertion in a previous topic and you have not replied. I assume, therefore, that you are unable to do so. In that case there is nothing to argue the toss about. The T rule applies.

So you are asking me to educate you??
Maybe you could explain via a drawing the reason WHY the HW cylinder return should be the connection nearest the boiler , what would be the issue if the common heating return were to be the connection nearest the boiler?
Obviously ALL heating returns would be joined before entering the common return unless individually zoned.
Does your RULE apply when using a LLH?..or possibly a ring header?