Cool radiators, new pump needed?

[bracken78]

Any plumbers in the house? I might or might not have a problem, I just don’t know, the radiators just don’t get very hot.

We have a combi boiler in the kitchen and a hot water tank in the bathroom. There are 7 radiators in the house which is around 100+ years old but I don’t know the ago of the boiler/radiators however the hot water tank has a date on it, year 2000. Since we moved in back in May my partner has always complained that the shower is not hot enough. I however have the setting on 5 out of 10 so thought the hot water was fine. The boiler was service in February and has a PCB board replayed but I’m not sure what the PCB board is?

I have been doing some basic tests with the radiators since first turning on the system last weekend. At first I had all the setting at max + and you can touch and hold you hand on the radiators and don’t get burnt, also the radiators are a constant temperature all over, the top and bottom are the same and there is no are in them. Last night I turned off all the radiators except the 3 on the ground floor and they didn’t get any hotter than before and the others stayed cold.

After my test last night I turn the boiler setting from around 8 out of 10 to max temp to see what happened. The shower and towel radiator was hotter, but again, not that hot. I don’t see why the boiler should have the setting on max, this must be really uneconomical.

I’m not sure why the radiators don’t get very hot but am guessing the boiler could need a new pump? As we are planning on being in the house a while think it might be work just getting a new boiler and power flushing the radiators/pipes instead of just repaving part on this old boiler every year.

Does anyone have any other ideas?

[John MacK]

Generally if the pump isn't working then the boiler would only run for short periods as it would keep tripping out on temp, and the pipes around the pump and out to the first rad etc would get hot, but the farthest away rad would be stone cold.

Maybe you need a flush and de-scale.

You should also be able to hear if the pump is running, does it have 3 speeds? Normally changing the speed setting will allow you to hear the motor change speed. Have you bled the pump?

[VR6time]

Bleed radiators.

If no luck, Drain and re fill system a few times.

[cjs]

You say you have a combi boiler and a HW tank, are you sure you have a combi boiler? They do not usually have a tank. What make model boiler do you have?

[bracken78]

Thank you for your replies.

I thought a combi boiler did both HT and CH, guess that’s wrong. I will have to check the name when home.

I forgot to mention but the boiler will only run for a few minutes and then cut out and the box the boiler is in gets very hot. I will recheck the temp of each radiator tonight but I’m sure they where all the same cool temperature. Maybe a flush and de-scale could help and I’ve not seem and pump speed dial, it seems a rather basic boiler. I have not bled the pump. I’m a bit new to boilers so will have a look.

Radiators are all bleed and I could not find anymore air.

[John MacK]

bracken78 said:

I forgot to mention but the boiler will only run for a few minutes and then cut out and the box the boiler is in gets very hot.

Sounds like it could be the pump.

Can you check if you are getting the correct voltage to the pump?

Check that there are no other restrictions in the system, e.g a shut vale beside the pump (if there are any)

A new pump shouldn't cost too much and is a reasonably straightforward DiY task.

[bracken78]

John MacK said:

bracken78 said:

I forgot to mention but the boiler will only run for a few minutes and then cut out and the box the boiler is in gets very hot.

Sounds like it could be the pump.

Can you check if you are getting the correct voltage to the pump?

Check that there are no other restrictions in the system, e.g a shut vale beside the pump (if there are any)

A new pump shouldn't cost too much and is a reasonably straightforward DiY task.

Hi and thank you for your reply John,

I can check the voltage but not until the weekend.

I've not been able to find any shut valves outside the boiler on the pipe work but I've not had the front of the boiler yet.

My thoughts where to just see if a new pumps fixes the problem if not maybe just put a new boiler in. Extreme I know but would rather pay out now than in 3 years time.

Henry

[Dogwatch]

Circulation pump won't have a dial, it's normally a 3-position switch (OK it could be in a dial form). If, as mentioned above, the pump speed is too slow the hot water generated by the boiler won't be pumped away from it fast enough so the boiler cuts out.

[AlexanderV8]

I had a pump whose impeller stuck once. I could get a large screwdriver on the slot in the middle (it was behind a small black cover in the centre if I remember correctly). A few sharp twists and taps with a small hammer got it free & it started spinning again. Stayed working for years.

Other things to check after turning the heating on for the first time after the summer are possible sticking pins in the thermostatic valves on the radiators. They tend to stick in one position. Take the valves off & you should see a pin. This should be free to move up & down to alter the flow through the radiator as set by the thermostat. I ususlly give mine a bit of oil & then a gentle tap with a small hammer, which usually frees it up.

I've got valves on all my radiators but also a room stat in the hall. I always forget about that one, as it seems odd to me to have both. Just check you don't have a room thermostat somewhere set low confusing things!

[spikeyhead]

I'd check what temperature the tank thermostat is at. Probably just needs turning up.

[bracken78]

Dogwatch said:

Circulation pump won't have a dial, it's normally a 3-position switch (OK it could be in a dial form). If, as mentioned above, the pump speed is too slow the hot water generated by the boiler won't be pumped away from it fast enough so the boiler cuts out.

Check and the pump is set in the correct position after reading the instructions.

AlexanderV8 said:

I had a pump whose impeller stuck once. I could get a large screwdriver on the slot in the middle (it was behind a small black cover in the centre if I remember correctly). A few sharp twists and taps with a small hammer got it free & it started spinning again. Stayed working for years.

Other things to check after turning the heating on for the first time after the summer are possible sticking pins in the thermostatic valves on the radiators. They tend to stick in one position. Take the valves off & you should see a pin. This should be free to move up & down to alter the flow through the radiator as set by the thermostat. I ususlly give mine a bit of oil & then a gentle tap with a small hammer, which usually frees it up.

I've got valves on all my radiators but also a room stat in the hall. I always forget about that one, as it seems odd to me to have both. Just check you don't have a room thermostat somewhere set low confusing things!

I will check the valves tonight, not done this before and also the thermostat is set at 20 just while I’m testing the system.

spikeyhead said:

I'd check what temperature the tank thermostat is at. Probably just needs turning up.

Check last night before we went out and it was set at 70 (went from 10 to 100). We moved the diel up 10 to 80 and the shower was much hotter this morning which is good. I’ve not tried the heating yet but will see if this changes anything one I’ve chackl the valves.

Thank you for all your help and I will updated tonight/tomorrow morning.

[page3]

AlexanderV8 said:

I've got valves on all my radiators but also a room stat in the hall. I always forget about that one, as it seems odd to me to have both. Just check you don't have a room thermostat somewhere set low confusing things!

That's a good point.

Anyone know if it is better to set the room stat in addition to the radiator thermostats, or just leave the room stat on max?

I have my room stat set to around 21, and the radiator stats set too (usually to 3 or 4 - whatever that equates to) but have never thought if this is the best (or most efficient) way?

[AlexanderV8]

page3 said:

AlexanderV8 said:

I've got valves on all my radiators but also a room stat in the hall. I always forget about that one, as it seems odd to me to have both. Just check you don't have a room thermostat somewhere set low confusing things!

That's a good point.

Anyone know if it is better to set the room stat in addition to the radiator thermostats, or just leave the room stat on max?

I have my room stat set to around 21, and the radiator stats set too (usually to 3 or 4 - whatever that equates to) but have never thought if this is the best (or most efficient) way?

I've always regarded the room stat as the control for the overall maximum house heat requirement from the boiler - ie. the level of heat the boiler will try & maintain by cycling around that set temperature. The thermostatic valves on my radiators are purely mechanical and so presumably are more of a 'fine' control for individual rooms. They surely can't allow more heat than that on the overall system set by the room stat (and boiler temp) but they must be able to allow less.

Although I'm not a plumber, I would think system efficiency would be influenced by the actual position of the boiler temperature control setting, in conjunction with the room stat. I tend to try & keep my boiler control about half way, with around 20 to 22 on the room stat. and then set the individual rooms by the thermostatic valves.

The thing that is confusing me is that if you were to turn all the radiator stats right down but kept the other controls as they were, the system wouldn't flow but the boiler would still want to heat the house! I wonder if this could overwork the boiler and pump - surely the pump would still want to work but the water wouldn't be flowing freely and so it could stress the motor?! I suppose this situation hardly ever happens but it would be useful to know the answer.

Let's see if a plumber comes along to help us out!

[Ferg]

For efficiency I would set the boiler at abouit 80 degrees flow temperature. The TRVs should be set to personal preference in the rooms and the Room Thermostat at about 21-ish. The important thing is to make sure the radiator in the same space as the Room Thermostat is cranked down on the lockshield end to get hot LAST. This is why we put them in hallways because there are more 'air changes' here.

As far as the cycling goes, this is why a Room Thermostat is crucial. If you don't have one the boiler will do this job by comparing flow and return differential...which is less efficient. You should have a differential pressure bypass really, but many people don't fit one if you have a three port valve since there can be no 'no-flow' situation with one (provided there is one radiator without a TRV (which is part of the Part 'L' efficiency regulations). The problem here is that as mentioned above, that radiator will most likely be cranked right down and most boilers require at least 10% of the heating load for bypass under pump-overrun situations.