Multi-Fuel Boiler not heating both hot water & radiators.

[CliveM]

Hi
I currently have an old cottage with a single pipe vented heating system, run off of a woodburner (multi-fuel). System gravity fed by header tank in loft with immersion tank and circulation pump for the radiators. I recently had to swap out the old woodburner, due to age of the old one, but the new version (10.5kw) is not man enough to heat both water and radiators. The water heating is gravity fed and gets hot enough to make a cup of tea, but the radiators only just get warm.
My question is, would it be feasible to put a valve in the 28mm hot water feed from the boiler, so that it by-passes the hot water tank and fed back into the cold return?. Obviously valve would be after the vent pipe on the rising hot flow.

Does this make any sense?

Any help appreciated.

Clive

 

[Ric2013]

Is there a typo in your second paragraph?

You want to bypass the hot water cylinder on the boiler flow and... not sure what you mean by the next bit!

 

[Ric2013]

More to the point, if the radiators are only just getting warm while the cylinder is almost boiling, I'd be looking at a circulation issue on the heating side. At least the pipes flowing into the radiators should be about as hot as the water leaving the boiler.
Can you confirm your radiators are plumbed as a 'One pipe system' - like this:

?

 

[CliveM]

Is there a typo in your second paragraph?

You want to bypass the hot water cylinder on the boiler flow and... not sure what you mean by the next bit!

Hi
Sorry I'm a bodging DIYer so haven't got all the technical spiel.
Yes, basically I want the option to bypass the hot hot water cylinder when more heat needed in the radiators and likewise turn off the bypass if I want more hot water. The system is currently vented with a 15mm pipe back to the header tank. System won't cope with doing both with any success.
Is it safe to do this with a multifuel system and where should I put the bypass?

 

[CliveM]

More to the point, if the radiators are only just getting warm while the cylinder is almost boiling, I'd be looking at a circulation issue on the heating side. At least the pipes flowing into the radiators should be about as hot as the water leaving the boiler.
Can you confirm your radiators are plumbed as a 'One pipe system' - like this:

?

Yes it is a one pipe system, with a circulation pump under the floor just before the cold returns to the boiler.

 

[Ric2013]

My thinking is that a bypass would not be considered safe as there is considered to be a need for a gravity-flow heat leak (which could potentially be a radiator running on gravity and used as a bypass if that radiator is large enough). I realise you still have the open vent which finishes over the header tank in 28mm (?) but then you may have no gravity circulation whatsoever, or does the heating run on gravity with the pump simply as a boost?
Also, safety aside, I don't think you'll gain anything as, once the hot water cylinder is up to temperature, it really won't be taking very much of the boiler heat output at all!
And you are sure that there isn't a flow problem - pump is definitely spinning and pushing water and the heated water is flowing quite fast into the radiators, but there are so many radiators that wate comes back almost cold? I'd have thought that at least the first radiator would get properly hot...

Hang on... am I right to assume that the gravity piping to cylinder is connected to the boiler, and that the pumped rads also are connected to the boiler?

 

[deg]

Pipe stat at the cylinder to kick the pump on once the hot water is satisfied. Anything after this is a circulation problem

 

[SimonG]

What you need is it piping properly and safely. Sorted.

 

[Ric2013]

Pipe stat at the cylinder to kick the pump on once the hot water is satisfied. Anything after this is a circulation problem

If the OP doesn't switch his heating pump on until the cylinder is hot through, he would get the same result (albeit manually). I know you know that, but I'm making this comment for the benefit of the OP.

 

[CliveM]

If the OP doesn't switch his heating pump on until the cylinder is hot through, he would get the same result (albeit manually). I know you know that, but I'm making this comment for the benefit of the OP.

Hope you can see this amateur drawing of my system.
Nothing is automatic about this antiquated system, if I want the radiators to get hot I have to manually switch on the circulation pump. One or two of the radiators upstairs get mildly tepid through gravity but not so you would notice. Radiators fed by 15mm pipe off the 28mm flow from the boiler. All hot water gravity fed, no fancy switches to shut off when up to temp, the hotter the woodburner, the hotter the water. Rads still only get warm never hot.

 

[Ric2013]

Clive,

That vent should be in 28mm, not 15mm, for safety reasons and you should get someone in, but won't be the cause of the radiator problem . Radiator pipes on 15mm okay.

If your drawing is correct, the pump will be pumping to the left. If it was working before, the pump direction isn't the current problem.

If you fire the burner until the cylinder is nice and hot and then turn on the pump, is there an obvious and immediate increase in the temperature of the water going in to the first radiator such that the pipe running into that first radiator is, as near as you can tell, just as hot as the pipe coming out of the top of the boiler?

Second question: is 10.5kW the total heat output for your new stove out of interest?

 

[CliveM]

Clive,

That vent should be in 28mm, not 15mm, for safety reasons and you should get someone in, but won't be the cause of the radiator problem . Radiator pipes on 15mm okay.

If your drawing is correct, the pump will be pumping to the left. If it was working before, the pump direction isn't the current problem.

If you fire the burner until the cylinder is nice and hot and then turn on the pump, is there an obvious and immediate increase in the temperature of the water going in to the first radiator such that the pipe running into that first radiator is, as near as you can tell, just as hot as the pipe coming out of the top of the boiler?

Second question: is 10.5kW the total heat output for your new stove out of interest?

Morso 1630 Dove

See link above to my boiler.

All of the radiators do get warm with the circulation pump on, just not hot, and no where near as hot as the hot pipe coming out of the boiler.

 

[CliveM]

For info currently running 1 large radiator, 4 medium and 2 towell rails.

 

[Ric2013]

10kW boiler, according to the spec. That's more than my gas boiler at home can do! Though don't quite see how a 10.5kW stove can have a 10kW backboiler... but that's Morsø's technical documents for you. Nice stove though.

From what you are telling us, I can't really see how that stove, run flat out, can fail to be reasonably sufficient once the cylinder is satisfied. You could look up the outputs of your radiators if you want to be sure and add it up (compare the sizes and type (single or double, with or without fins) with manufacturers' or retailers' data), but I doubt that's the problem you have.

If none of the radiators are getting hot water as hot as the boiler, then I'm really of the opinion that there must be a problem with the water not being able to get around the system due to air, limescale, or sludge rather than the new boiler being insufficient. If the boiler were insufficient then I'd expect to see the entire system, including the boiler itself, running at a low temperature. I note your drain point is above the lowest point - could be that when you drained down all the muck fell to the bottom. Pump could be full of rubbish or airlocked?

I'll shut up and leave others to comment now, but I'm thinking flush through rad circuit with a hose, check pump is working properly and on fast enough speed, and get a plumber to sort out that 15mm vent.