After new rad fitted boiler doesn't want to switch on

[diy_massacre]

Hi

Could you give me some advice based on the following points below?

System background (small cottage) it has
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• System Gas boiler ground floor Greenstar Ri think its a 15;
• Two gravity fed header tanks in the loft one small one for the radiators and the other much larger for cold water
• 3 rads downstairs and 4 rads upstairs, 3 beds and bathroom.
• Indirect hot water hot tank on first floor.
• Everything is pretty normal in my book except the rads are run off 8mm tubing which I have never seen before and most rads are run from the loft. system boiler has 22 mm pipes which they transpose to a 22mm to multi-output 8mm type distribution pipes,

What actions I took to change
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• Its all worked well until I drained the system today, closed the stopcock to the small tank in the loft.
• Fitted a new radiator in the master bedroom. Really I swapped the old one for a new one and repiped the new one to the older pipes. This was to put the bed up against the wall.
• After fitting the new radiator I opened the stopcock to the small header tank and bled all the radiators and opened all the values. I also bled the cock above the boiler in case I any air came out. There was appropriate gurgling when bleeding the rads.

Outcome / Problem
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• The boiler comes on but and starts making starting sounds but then closes down. The output pipe of the system boiler is hot so it's working correctly.
• Hot water or heating doesn't work.

Please can you advise what you think it wrong, I dont believe I am able to bleed any more radiations, have looked at numerous posts but they have not resolved the issue.

Kind Regards

Matt

 

[ShaunCorbs]

Air locked shut all but one rad upstairs closet the boiler or airing cupboard

Then turn the heat on doesn’t matter if the boiler doesn’t fire you will hear a load of air move and you will need to bleed the upstairs rad that’s still on

Then repeat for the rest once that ones hot

 

[John.g]

System or boiler HX may now be clogged with sludge after drain down but hopefully not if water was clean before draining. It may be air still trapped somewhere, if external pump fitted have you vented it by slackening the vent screw (if fitted). Also suggest turning up pump speed to max for awhile (after noting original setting).

 

[Ric2013]

You say the outlet pipe gets hot. This suggests a mimimal movement of water. I'd expect the outlet to be hotter than the inlet but for the whole to get progressively warmer were it flowing properly. Almost certainly a circulation issue and I'm with Shaun on this (as usual). Airlocks are not uncommon with open-vented systems. If you can turn up the pump without contravening gas laws, then do, as John.g has suggested.

If you have a small tank in the loft for the radiators, then you very probably do not have a system boiler. As a system boiler contains the pump and an expansion vessel. Something in your description does not add up.

 

[SJB060685]

Vent the pump first off.

 

[diy_massacre]

You say the outlet pipe gets hot. This suggests a mimimal movement of water. I'd expect the outlet to be hotter than the inlet but for the whole to get progressively warmer were it flowing properly. Almost certainly a circulation issue and I'm with Shaun on this (as usual). Airlocks are not uncommon with open-vented systems. If you can turn up the pump without contravening gas laws, then do, as John.g has suggested.

If you have a small tank in the loft for the radiators, then you very probably do not have a system boiler. As a system boiler contains the pump and an expansion vessel. Something in your description does not add up.

The outlet temp of the boiler is very hot but the inlet not, but the inlet is not. Thats consistent with the boiler being turned on and off for a short while.

There is a pump in the loft so will have a go at venting it, it was already on max power.

Ii totally agree with the circulation conclusion, the water was mostly clean apart from one rad.

Thanks for the point on a system boiler I thought it was.

 

[diy_massacre]

You say the outlet pipe gets hot. This suggests a mimimal movement of water. I'd expect the outlet to be hotter than the inlet but for the whole to get progressively warmer were it flowing properly. Almost certainly a circulation issue and I'm with Shaun on this (as usual). Airlocks are not uncommon with open-vented systems. If you can turn up the pump without contravening gas laws, then do, as John.g has suggested.

If you have a small tank in the loft for the radiators, then you very probably do not have a system boiler. As a system boiler contains the pump and an expansion vessel. Something in your description does not add up.

Hi Ric,

The external pump in the loft went well and I can hear the pump working and some bubbles shooting through the pump.

Unfortunatley the boiler still closes down after 30 seconds of operation, either for hot water or central heating.

Any other ideas?

Best Matt

 

[John.g]

I would connect the pump to a independent power supply (extension lead), switch off the boiler and keep circulating water with continuous venting "everywhere" or/and as suggested shutting off most of the rads selectively until air expelled. What is the vent & cold feed arrangement? because (if its) the combined type are notorious for entraining air when refilling unless its done extremely slowly.

 

[diy_massacre]

I would connect the pump to a independent power supply (extension lead), switch off the boiler and keep circulating water with continuous venting "everywhere" or/and as suggested shutting off most of the rads selectively until air expelled. What is the vent & cold feed arrangement? because (if its) the combined type are notorious for entraining air when refilling unless its done extremely slowly.

Hi John,

Thankyou for responding!

When I switch the boiler on HW or CH setting the pump in the loft goes on and stays on despite the boiler shutting off after 30 seconds, so dont think I need a separate supply to keep the circulate the system going as it stays on from a separate electronic controller. Is that right?

I will try shutting off all the rads selectively, and try and track down the air pockets for each rad independently, will come back on this one...

"What is the vent & cold feed arrangement?" - If I understand you correctly the radiator cold feed arrangement comes from the small header tank and there is an overflow pipe hovering over it, I suspect this is the expansion/ aerator refill pipe not but 100% sure. The cold water for the taps is fed from a larger cold water tank.

"when refilling unless it's done extremely slowly" - I dont understand your comment isn't there only one speed to refill the system from the header tank?

Many thanks Matt

 

[John.g]

Pump running constantly probably OK.
Combined vent&cold feed as shown.
When refilling the system, open the (empty) header outlet valve first then tie up the ball cock to allow a trickle of water to flow, this helps to allow the air to vent and the water to flow through the same (combined) pipe. I have a isolating gate valve on my system so I can just crack it open to control the water to the ball cock.

Is there a vent plug in the centre of your circ pump?? you might post a picture of your pump showing the model details etc.