Cold Radiators

[redcap]

Had a new indirect cylinder fitter during last summer and since the central heating system has an intermittent fault whereby I struggle to warm them up sufficiently.

It appears there maybe an air lock somewhere in the pipework.

Today for about the third time, I have completely drained the whole system, shut down all rads both upstairs and downstairs, refilled, balanced and bled all radiators, opening the one nearest the downstairs boiler and gradually working outwards with the downstairs rads only.

They worked to half capacity for about two hours then suddenly all of the ones started (8) all went cold although the boiler was still functioning,

Recently fittd a new pump which is scalding hot to touch and hot tap water also is scalding hot.

Is the next step to gently pressure the system in reverse using a mains hose pipe? If so I would welcome advice.

The cylinder was replaced by a professional, is it possible to connect the flow and return incorrectly and if so would this be the possible cause of my problems?

Colin (redcap)

 

[jackthom]

Is the pump set to the max speed?
Also there is probably a mid position (3-port) valve in the system and it may be worth checking that it goes to the central heating only position when heating is on and hot water isn't required (you can force it there manually if necessary). That way the maximum flow will be directed around the radiators which may help shift any air in the system.

 

[75pete]

You say that you had a new HWC fitted, It could be that the balancing valve on the HW system is full open. Try shutting it and then reopen, say 2/3 turns.
It will take longer for your HW to heat but will increase flow to the rads.

Check the stat on the HWC, reset it to say, 55f. It must make face to face contact with the copper of the tank to work.

And as jack say`s , check the valve[3port] as it maybe the problem.

 

[redcap]

Thanks Jackthom for your quick reply.

The pump is set at max 3 position.

The boiler is a Potterton Kingfisher MF/CF60 so where would I find the 3 way valve?

I was about to carefully blow the system backwards using a clamped hose from the main tap, would this be better done with all rads switche off or on?

Colin (redcap)

 

[redcap]

Thanks Pete but where is the balancing valve generally located?

There is a valve on a 22mm pipe which appears to connect the header tank to the back of the HWC at the bottom.

The old tank had a thermostat which was fitted by the plumber that installed the new boiler about 3 years ago, but my new plumber said they are more trouble than they are worth and did not fit one to the new HWC.

From what you are saying, your observations could well be the problem.

Colin

 

[jackthom]

Untitled

• jackthom
• 19 Dec 2008
• 18

The valve would usually be in the flow from the boiler just after the pump where the feed splits in two, one to the DHW cylinder and the other to the radiators.

EDIT: just spotted your last post and if there's no cylinder thermostat there won't be a mid position valve.
It's likely a large proportion of the flow from the pump is short circuiting through the DHW cylinder leaving very little hot water pushing through the central heating.

 

[D_Hailsham]

The boiler is a Potterton Kingfisher MF/CF60

How many pipes connect to the boiler - not including the gas pipe?

 

[redcap]

Have front panel off boiler and cannot see any 3 way valve similar to the photo, the Wilo pump is fitted externally and both flow & return appear to dissapear behind the boiler, but by using a mirror with a torch cannot see this valve anywhere.

There are three 22mm water pipes connected towards the top at the rear.

Just to note, the whole system has worked perfectly throughout the house (18 rads) for last three years and the problem has only occured since the new indirect HWC fitted last summer.

Could the problem be directly related to not having a HWC thermostat fitted as the HW is scalding hot as is the surface of the external pump, yet although the pump appears to be functioning correctly as of this reply all the rads are stone cold.

There is obviously air in the pipework, so If I reverse pressure the whole system, would this help?

Colin

 

[twgas]

3 port valve would not be inside boiler, usually they are next to cylinder, although, only yesterday I had one where the MV was next to boiler.
MFs only have 3 tappings so this could be misleading and you may have gravity hot water. Are there any tees in the pipework near the boiler?

 

[redcap]

Thank's for your input Mick, as far as I can see there are no "T" junctions in the pipework at the back of the boiler and my HWC is upstairs therefore am I to assume that the HW is gravity fed?

Have done a slight back pressure by connecting mains hose to drain off stop cock and did manage to get 8 downstairs adjacent rads to work to 80% efficiency last night before turninf off. This morning everything appeared to be functioning as expected.

Something is adrift as I have had everything working before then suddenly all the rads are cold - I keep my fingers crossed and live in hope!

Colin

 

[D_Hailsham]

Thank's for your input Mick, as far as I can see there are no "T" junctions in the pipework at the back of the boiler and my HWC is upstairs therefore am I to assume that the HW is gravity fed?

If you have three water pipes connected to the boiler, it will be gravity hot water. This uses a common feed for the rads and HW cylinder, which must split into two branches at some point, a pumped branch for the rads and un-pumped for the HW. The other two connections are the return from CH and return from HW. If there is no motorized valve in the HW circuit, then the HW temperature will be determined by the boiler temperature. The CH thermostat will control the pump, which then acts as a valve on the CH circuit.

You have two options:

1. Insert a motorized zone valve into the HW circuit, controlled by a thermostat on the HW cylinder. You can then turn the boiler stat up to max as the HW temperature will be controlled by the stat on the HW cylinder closing the zone valve. This is called a C-plan system.

2. Convert to a fully pumped system, with either a mid-position valve (Y-Plan) or two zone valves (S-Plan).

 

[redcap]

Thank's for your very detailed and explanatory advice which I will probably act upon to improve the system generally.

Today is the second full day since I restarted the system and so far "touch wood" it appears to functioning OK, I have 8 out of 10 rads on downstairs and 1 in bathroom upstairs which is my normal requirement, so hopefully my good fortune will continue.

A big thankyou to everybody that has given advice, it's much appreciated, if however my luck runs out, I will be back for more advice.

Happy Christmas and a better New Year to all.

Colin