Central Heating Problem

clonshanny

Hi all, Can someone please help.
My father in-law who lives in a bungalow has a problem with his rads not heating. He had 2 systems linked, one from the range and the other from the oil boiler. We recently separated them after he replaced the range with a stove. The plan was that the stove with its small boiler would heat the domestic hw cylinder and one rad by gravity, and the oil would heat the rest of the rads and also the other coil in the dhw cylinder. Problem is that the oil boiler is only heating the coil in the dhw cylinder and not heating the rads. We've got a gate valve on the flow pipe to the cylinder and when i closed this some of the rads began to slowly heat but not sufficiently. We dont have a motorised diverter valve where the flow pipe to the cylinder branches. Would this be the problem or is there something more serious wrong? Any help greatly appreciated.

Jedstaff

Check if the pump is circulating. Cylinder might still heat on gravity.

clonshanny

The pump is working fine Jedstaff. Its located in the boiler house and the pipes run under the floor from there. As the flow pipe from the boiler has to drop and then rise again to the coil, I dont think the coil in the cylinder would heat on gravity if the circulating pump didn't work. As far as i know, the theory behind gravity or convection as its sometimes called, is that once it drops, it cannot rise again.
I'm puzzled as to what it could be.

DoneDL

when the oil heating is running does the stove get hot?

clonshanny

No it doesn't DoneDL. The stove is solid fuel and its piping system is completely separate from the oil boiler. The only place they come close is in the dual coil cylinder.

DoneDL

sorry just read your post again, systems aren`t linked. The boilers running so heat is being produced, was the system drained down at any stage and is there water in all the rads and boiler. Does the boiler cut out quickly or keep running,

clonshanny

The system was drained when we took out the range and put in the stove. It was empty for over a week. All rads are full with water because we bled each one when we refilled the system. The stat on the boiler cuts the boiler out quickly becaues with the water not circulating through the whole system, it reaches the set temp very fast.

DoneDL

When the heating is on is the pipework on both sides of the pump equal in temperature.

clonshanny

Yes, its very hot. Even in the hotpress the flow pipe gets to the same temp but its where it branches off in different dirrections to the rads seems to be the problem. It just seems to slow down somewhere under the floor and not travel to the rads as quickly as it should. Would it be a balancing problem?

clonshanny

clonshanny wrote: »

Yes, its very hot. Even in the hotpress the flow pipe gets to the same temp but its where it branches off in different dirrections to the rads seems to be the problem. It just seems to slow down somewhere under the floor and not travel to the rads as quickly as it should. Would it be a balancing problem?

Sorry, its hardly a balancing problem when there is just one 3/4" flow and return with 1/2" branching to each rad indivdually.

DoneDL

Sounds like an airlock or blockage, turn the boiler off and connect a power supply to the pump so it runs continously and see if this clears it. Its is easier to clear an airlock when the system is cold. Try varying the pump speed.

clonshanny

I put some heat into the water from the boiler this morning and then turned off the boiler and let the pump run for a while on its own like you said. It still took ages for the hot water to reach the rads. I've also noticed that when i closed the gate valve to the coil in the dhw cylinder, the pipe above the valve continued to heat and also the return from the coil. Seems like the gate valve isn't preventing the heat rising to the coil.
In your opinion, should i leave the pump running for long while the water is cold?

DoneDL

It sounds like the gate valve is letting by, close it off as best you can and try the pump at speed 3 for a while to see if it push the water through.

clonshanny

Thanks for your help DoneDL. Think I've got is sorted. Well, part of it anyway. I let the circulating pump run for ten minutes or so and then opened the bleeder on the boiler. Some air came out of it so i repeated the process again and got some more air. Did this about ten times until i didn't get anymore air. Then left the pump rinning for about an hour or so on its own. When i went back, i tried the bleeder again but no more air so i turned on the boiler. Had the gate valve on the flow pipe to the coil in the dhw cylinder completely closed. All the rads heated fine this time with no heat travelling up the flow pipe to the coil in the cylinder. All the rads got to max temp fine so I opened the gate valve slightly to let some hot water into the coil. It didn't seem to be flowing too well so i opened the valve some more until the return pipe heated too. The boiler was off when i went back to it so i dont know if it was because i opened the gate valve or because the all the rads were hot and the stat was knocking out the boiler. Will have to let the system cool again and try the boiler with the gate valve in the position its currently in. Fingers Crossed.

DoneDL

Nice one clonshanny, when its running properly don`t forget to rebalance the system as it will save on your oil.