Central heating puzzle.

[Dee J]

This may be one of those 'observations are wrong or incomplete' issues, but please bear with me. System is a few years old, but used to work fine (so not an install issue).
Wet central heating system (rads) running from Ideal Logic+ boiler (combi hot water works fine).
Stat calls for heating, boiler fires, radiator feed heats up, and very soon after the radiator return pipe is very hot too. Great, you'd say, job done. Except that no radiator (including the presumed bypass) is returning anything that hot (barely warm in fact).
So there has to be a return path other than rads.
I've just found out about auto bypass valves, but if one is installed here, where to look? Is this a likely scenario that everything is returning via the bypass, with very little through the rads?

 

[dave h 2]

Mines just after the pump

 

[Dee J]

Mines just after the pump

Thanks. On mine both pipes are visible for a short distance before disappearing under some chipboard flooring in the airing cupboard. Time to break out the endoscope!

 

[hotponyshoes]

Does the boiler heat a hot water tank as well?
If so, just turn the heating on and see if the tank starts warming up.
Check the 3-way valve if it does.

 

[dave h 2]

Thanks. On mine both pipes are visible for a short distance before disappearing under some chipboard flooring in the airing cupboard. Time to break out the endoscope!

The pump should be accessible.

 

[Dee J]

The pump should be accessible.

Pump is part of the boiler (or at least inaccessible to me in the boiler casing). So I'm just left trying to diagnose with the boiler as 'black box'. That said, the issue is external to the boiler. Rad feed is hot going out, and return is quickly hot too. So something external to the boiler is acting as 'short circuit' - that's why thoughts of (hidden) bypass valve comes to mind.

 

[gaz1]

This may be one of those 'observations are wrong or incomplete' issues, but please bear with me. System is a few years old, but used to work fine (so not an install issue).
Wet central heating system (rads) running from Ideal Logic+ boiler (combi hot water works fine).
Stat calls for heating, boiler fires, radiator feed heats up, and very soon after the radiator return pipe is very hot too. Great, you'd say, job done. Except that no radiator (including the presumed bypass) is returning anything that hot (barely warm in fact).
So there has to be a return path other than rads.
I've just found out about auto bypass valves, but if one is installed here, where to look? Is this a likely scenario that everything is returning via the bypass, with very little through the rads?

Pump is part of the boiler (or at least inaccessible to me in the boiler casing). So I'm just left trying to diagnose with the boiler as 'black box'. That said, the issue is external to the boiler. Rad feed is hot going out, and return is quickly hot too. So something external to the boiler is acting as 'short circuit' - that's why thoughts of (hidden) bypass valve comes to mind.

if you dont have a hot water cylinder then your rads could have air in them

feed in and output gets red hot means air in the system as it direct flows at bottom of the rad this is where bottom of rad gets hot only

as goes for your system reset your system that means open and close all valves and then rebalance your system it cancels the quick feed back via the return pipe
whilst you rebalance your system check which side the flow is

 

[Kayos]

Internal diverter jammed

 

[Jaeger_S2k]

Possible pump failure, switch to tell the pump to run failure?

 

[Dee J]

Well here's a puzzle. Pipes to the bottom left of the image are boiler feed and return. To the left are pipe to radiators. Centre of the picture is the offending short circuit. Stubs to right used to go to a long-disconnected back boiler. Now the puzzle is not so much why it doesn't work now, but how it's ever worked since the back boiler was removed.

 

[dobbslc]

Is there possibly a zone valve somewhere hidden that's stuck over the summer?
Check to see if the boiler return pipe is getting hot by conduction rather than water flow ie is the pump knackered and the pipe just getting hot near the boiler?
Does that loop under the floor get hot before or after the bit of pipe next to the boiler?

 

[Dee J]

Whole loop to short circuit and return heat up very quickly when boiler fires. Definitely heating by pumped water flow, not conduction. Tiny flow to radiators to the left. No zone valves. Only 5 rads in a small terraced house. 4 rads have trv, one just valves - so I'd assumed that was the bypass.

 

[OJCar]

Had similar in our property in Cumbria.
Try putting a gate valve in the short circuit and set it partly closed.
If the radiators heat normally you've identified the issue.
Plumb a radiator to replace the short and enjoy heat!

No idea what the "plumbers" had been smoking...

 

[Morrisman]

if you dont have a hot water cylinder then your rads could have air in them

Just found that with my bathroom rad, only small but totally cold, except the very bottom corners where water pipes connect. I assumed the TRV was stuck and planned to book a guy Homecare to fix it.

Then I thought to bleed it. Only 3-4 seconds air whistled out so I assumed that wasn’t the problem.

Ten minutes later the rad was red hot all over.

 

[voipio]

If there's one radiator with only valves on it, and no TRV, then that's the bypass. The short circuit under the floorboards can be closed off without issues, though @OJCar 's suggestion of putting a gate valve there gives an option to fine tune the system a bit, if needed. .

 

[Kayos]

If it worked it's a component fault

Knowing those boilers it's the internal diverter

******* about altering rads and adding gate valves is a waste of time

If you are confident, pull the case off and whip the diverter out

If you are not, call a heating engineer

 

[gaz1]

Well here's a puzzle. Pipes to the bottom left of the image are boiler feed and return. To the left are pipe to radiators. Centre of the picture is the offending short circuit. Stubs to right used to go to a long-disconnected back boiler. Now the puzzle is not so much why it doesn't work now, but how it's ever worked since the back boiler was removed.

thats an issue in the first place as its direct back to the boiler in full flow

in truth your system wasnt running properly whilst that system was used and shuts the boiler down due to heat returning back to the boiler quickly but your system isnt getting up to temp on your rads properly

ive also seen it done when an emersion heater has been removed

 

[dave h 2]

Just found that with my bathroom rad, only small but totally cold, except the very bottom corners where water pipes connect. I assumed the TRV was stuck and planned to book a guy Homecare to fix it.

Then I thought to bleed it. Only 3-4 seconds air whistled out so I assumed that wasn’t the problem.

Ten minutes later the rad was red hot all over.

Your problem there is the gas comes from rusting, the system needs more inhibitor.

 

[sg66]

Is your system so old it was originally a single pipe system that's now been half converted to a flow and return, do you have a flow and return going past each rad or is the flow and return taken from a single pipe.

If it's got a flow and return then that loop needs to go.

 

[Dee J]

Thanks all. Looks like there was a misinterpretation of the pipe layout when the backboiler was replaced by the combi. Will look at blanking off that loop entirely, or maybe fitting a bypass valve.