Central heating not getting very warm

[Bifta]

Hi all,

We've encountered a problem with our CH as the colder weather is getting more frequent.

The radiators don't seem to be getting very hot, and one remains completely cold.

We have a small two bedroom town house (terrace style in effect). One radiator in each main room, 5 in total.

The three radiators upstairs I can get to about 50oc, the one downstairs in the kitchen about 35oc, and the one in the living room, is the one that stays off.

Temperatures measured in the middle of the radiator at their tops.

I've bled and balanced the system and if I close down all the other valves, the living room rad will get warm but not hot.

We have TRVs on all rads, as well as lockshields on their other ends.

I've also tried to examine the pump, but when I remove the large screw on its front, too much water comes out for me to see what's going on inside it.

The boiler is a Baxi 105 e combi. Maybe 10 years old at a guess. I've been in the house for 5.

My thoughts on possible problems are:

1. Sludge in the system; do you think this is likely?
2. Worn pump
3. Possible faulty diverter valve, water passing through the hot water circuit

Should also mention that the boiler shuts off between 70oc and 80oc. It maintains pressure, although this is a nice change as there have been periods before when we've needed to top it up quite frequently. Do you think the expansion vessel could've failed completely and debris from such could be blocking the boilers internal pipework?

Any advice would be greatly appreciated

Thanks, Alex

 

[JohnD]

are the radiators cold at the bottom, or in the middle?

if you feel the flow and the return pipes on the boiler, when it is trying to heat the radiators, how hot are they? How hot is the pump, and the pipes beside it?

When the heating is off, and you run a hot bath, do any of the radiators warm up?

 

[Bifta]

They are a bit colder towards the bottom but still warm. I will get some temps tomorrow.

I know the flow pipe out of the boiler (just underneath) is really hot, like too hot to touch, as is the pump.

I will check re the return pipe, the pipes around the pump, and the bath scenario.

Thanks

 

[JohnD]

look for a bypass.

If the water coming out of the boiler is really hot, and the rads aren't, where is it going?

But if the return pipe is cool, you have a circulation problem.

Sediment-clogged rads are cold in the middle.

Water should not come out of your pump, when you take out the central screw, in more than a drip, or possibly dribble.

 

[Bifta]

Just done the bath scenario. The rads stay cold. The CH flow pipe becomes tepid but only close to the boiler, the pipe work connected to the pressure relief valve gets a little warmer than tepid but again, only close to the boiler and there isn't any water coming out from the end of it outside.

When I tried to inspect the pump before, I couldn't really take the big screw off because there was a constant leak coming from it when I did this and didn't want this leak getting into the boilers electronics.

Thanks again

 

[Bifta]

Ok, so the return pipe is a little warm. The pipes around the pump are very hot, at least those that I can touch are.

The three upstairs rads are 50oc top, 45 Middle and 40 at their bottoms

 

[jackthom]

It would be useful to know how hot the boiler return pipe feels just before the boiler has reached it's target temperature and cuts out.

 

[Bifta]

Ok Jack, does this need to be the first time it fires in a given heating period or at any time during that period?

 

[jackthom]

Probably best when the heating has been off for a while and the radiators are on the cool side.

I'm trying to find out if there's just insufficient flow through the boiler and it's maybe cycling on and off, even when the return water temp is not particularly hot.

 

[Terry lambert]

Go to the cold rad, take the TRV head off and check the pin underneath isn't stuck.

If it is; use a pair of pliers to gently pull the pin up.

Check the lock shield at the other end is open

 

[Bifta]

A bit more info:

The return pipe work is still cold when the boiler cuts out after its first cycle. The boiler doesn't actually fire for very long.

TRVs pins are all ok.

 

[jackthom]

Very poor circulation could be sludge, pump or both.

Is the boiler fitted with a 3 speed pump?

 

[Bifta]

Pump is a Grundfos UP 15-60 A0. I can't see any obvious speed control on it but there looks like there's a removable panel on the left hand side with a small screw in its centre. Would it be removing this to check?

 

[Gasguru]

Have a look at the return isolating valve assembly, under the cap on the front is a filter...prob just needs a clean.

 

[Bifta]

Untitled

• Bifta
• 4 Nov 2014
• 1

Just double checking I'm looking at the right thing before I start taking things apart.

The website has rotated the image so is the cover in question the one toward the middle left of the photo? Will much water come out when I remove the cap? Should I use the isolation valves? And I'll need a spanner right?

Thanks