Central heating cock-up - is there an easy fix?

[Shiralco]

We have a traditional vented C/H system with a boiler on the ground floor and an airing cupboard on the first floor containing the hot water cylinder and C/H pump feeding a Honeywell 3-way valve.

I asked a local plumber to fit a new radiator in a ground floor extension, but there was no easy way to access the existing C/H pipe work without emptying an upstairs room and taking up all the flooring, which we didn’t really want to do. Since the boiler was right next to the extension I asked if we could just T-off the two 22mm pipes from the boiler, go through the wall and connect directly to the radiator. OK, he should have known better, but he agreed and made the connections. He did point out that the radiator would be on whenever the hot water was on, but as it was fitted with a TRV, I didn’t think this was a problem.

Of course, it doesn’t work. He later admitted that he is so used to working with combi boilers that have the pump in the boiler, that he forgot that the T-off was upstream of the pump, and the new radiator is effectively short-circuited by the boiler. So the new radiator gets hot when the hot water is on, but cools down when the heating is turned on.

Is there an easy fix? Would fitting an additional C/H pump between the boiler and the T-off to the new radiator, either on the flow or the return, solve the problem? Both pumps would then switch on together and be in series, presumably assisting each other. Or would this cause a surge of water through the vent pipe? I don’t want to solve one problem and cause another.

Any suggestions would be appreciated – apart from rip it all out and start again!

 

[twgas]

Take the flooring up as first suggested, short cuts seldom work properly.

 

[Galoka]

It's unlikely you would be able to put a pump on the flow from the boiler before the T as that needs to be kept clear as it will be the vent pipe from the boiler.

It would have to go on the flow or return pipes to the new rad. But yes it would work then. You might need to use a manual valve as well to limit the flow down this pipe.

Another (maybe off the wall) thought, i wonder if an injector Tee on the boiler return (where the new rad return joins it) would maybe 'suck' enough water through the new rad circuit? They are typically used on solid fuel systems to ensure the correct circulation round the gravity HW circuit when the CH pump is operating.

A quick Google search will make it clearer

Or use electric heating in that room until you want to lift the floor?

 

[jackthom]

Yes if the pump was fitted after the tee on the flow to the new radiator it should work fine. It would probably be OK on the slowest setting and would only be required to power up when there was a demand for heating.

I'm not sure of the best way to prevent reverse flow through the radiator (bypassing the boiler) when only hot water is required. Maybe the stationary pump would present enough resistance or is there maybe a one way valve that would work at pump pressure?

 

[Agile]

Easy enough to and a non return valve.

That's how the Grundfos pump plan did it.

Tony

 

[Shiralco]

Thanks guys for all your replies. If I fit a pump in the flow to the new rad, what happens when the TRV turns the rad off? Will this damage the pump? Also, Agile, where can I get a copy of the Grundfos pump plan?

 

[gigz]

Thanks guys for all your replies. If I fit a pump in the flow to the new rad, what happens when the TRV turns the rad off? Will this damage the pump? Also, Agile, where can I get a copy of the Grundfos pump plan?

Fit an automatic bypass after the pump, connected to the return, this will open if the trv closes.

 

[ServiceNumpty]

All this work, why oh why don't you just empty the upstairs room and do it properly.

 

[gigz]

All this work, why oh why don't you just empty the upstairs room and do it properly.

Agree with this, it would have been worth it.

 

[Galoka]

Thanks guys for all your replies. If I fit a pump in the flow to the new rad, what happens when the TRV turns the rad off? Will this damage the pump? Also, Agile, where can I get a copy of the Grundfos pump plan?

Fit an automatic bypass after the pump, connected to the return, this will open if the trv closes.

Or forget the TRV, and switch the pump with a roomstat for that room.

 

[Shiralco]

Once again, thanks fellas for all your advice – plenty for me to think about. In the good old days you just rolled back the carpet, cut the tongues out of a couple of boards and you were in business. Nowadays you have ceramic tiles that cost more than my car, under which are 8 by 4 sheets of ‘modern flooring’ – that’s chipboard to you and me. And NO, before anyone suggests it, I am not going to take the ceiling down!

 

[jackthom]

Or forget the TRV, and switch the pump with a roomstat for that room.

Just another vote for this.

It's likely the new radiator will be getting more than it's fair share of hot water in this setup, so a room thermostat to knock off the new pump would seem an efficient solution if it turns out this room now heats up more rapidly than others.