A thermostatic mixing valve blends hot and cold water to a safe temperature before it reaches the tap, shower or bath. Left alone, it slowly drifts, scales up and gets lazy. Then one day the cold supply drops out and it doesn't shut off like it should. Servicing is how you stop that day happening.
What happens on a TMV service
Every valve gets the same routine, whether it's the only one in a Fulham conversion or one of four hundred in a Lewisham care home.
- Find it and record it. Location, make, model, type (TMV2 or TMV3) and the outlet it feeds. If you don't have an asset register yet, this is where it starts.
- Check the supplies. We measure the hot and cold coming in. A TMV can only mix what it's given, so a lukewarm hot supply or a warm cold supply gets flagged, because that's a wider Legionella control issue too.
- Measure the mixed temperature at the outlet and compare it with the set point for that outlet type.
- Fail-safe test. We isolate the cold supply and watch what the valve does. It should shut off, or drop to a trickle, quickly. Then we put it back and check it recovers properly.
- Strip and clean. Strainers out, check valves out, scale and debris off. In London that usually means a proper descale, not a quick rinse.
- Cartridge and seals. We descale the thermostatic cartridge or replace it if it's past saving, and swap tired seals.
- Recalibrate and retest. Set the outlet temperature, repeat the fail-safe test and record the final readings.
- Write it up. A certificate for each valve, the logbook updated, and a short list of anything that needs more than a service.
Hard water is the London problem
London's water is hard. You'll know this if you've ever looked inside a kettle in Clapham. Inside a TMV, the same scale coats the thermostatic element so it reacts slower, packs the strainers so flow drops, and stops check valves seating properly so hot and cold can cross over.
That's why descaling is part of every service we do here, and why we'll be honest when your interval needs to come down. A valve in a soft-water town might happily go a year. The same valve in a busy London shower block might need looking at every six months.
What we'll tell you: how scaled each valve was, whether the strainers were restricting flow, and whether we think your current service interval is right. If it isn't, we'll say so, with the readings to back it up.
How often should TMVs be serviced?
HTM 04-01, the Department of Health guidance for healthcare water systems, sets out the approach most people follow in other buildings too. A newly commissioned valve gets in-service tests at around 6 to 8 weeks and again at 12 to 15 weeks. After that, the interval depends on what the tests show.
- If the mixed temperature has barely moved, the interval can stretch out.
- If it has drifted noticeably, the valve gets serviced and the interval stays short.
Most London buildings end up somewhere between six-monthly and annual servicing. Hard water, heavy use and vulnerable users all push towards the shorter end. Your Legionella risk assessment and written scheme should say what your site needs, and we'll work to that. Our TMV compliance guide goes into the detail.
Your paperwork
After every visit you'll have:
- A service certificate for each TMV with the before and after readings
- Logbook entries you can drop straight into your Legionella records
- An up-to-date TMV asset register with locations and next due dates
- A priced list of any valves that need replacing, with the reason
Fitting it around a London building
Most of the valves we service are inside somebody's home, ward, classroom or hotel room. So we plan access with you, send notice letters to residents if you'd like, and book return visits for the rooms we couldn't get into. We sort parking before the day, and we can work early, late or in holidays if that's what the building needs. More on that in how we work.
Common questions
How long does a TMV service take?
Usually 20 to 40 minutes per valve once we can get at it. Heavily scaled valves and ones hidden behind tiled-in panels take longer. Access is normally the bigger factor in a London building.
Will the water be off while you work?
Only at the outlet we're working on, and only for the time it takes. We isolate locally wherever there are isolation valves. If there aren't any, we'll talk to you before we touch anything bigger.
What if a valve fails the fail-safe test?
We'll try to bring it back with a clean, descale and new parts. If it still won't shut off properly, we'll tell you there and then, make the outlet safe if needed, and give you a price to replace it.
Do you service all makes of TMV?
Yes, we service the common makes found in UK buildings. Some older or discontinued valves can't get parts any more, and then replacement is usually the sensible answer.
Got TMVs in London that need a look?
Tell us roughly what you've got and where. We'll give you a fixed quote and a date that works around your building.